So I can't turn on my Optiplex 755 through the regular power button. I have to hold the power supply test button on the back, and then press the on button. The computer then stays on, but I don't get any video output. No BIOS beeps or anything. Not sure what's going on. The service tag is
Power supply problem?
It does sound like there is a problem with the power supply but I've got some steps that will help you determine exactly what is happening. Some of these steps require opening the system so please remove the power cord from the back of the system before doing these steps. If you can answer the following, it would be a great help:
1) Switch the system on. Can you tell me the colour of the power button and also whether the power button is flashing or not? Please also tell me if you notice any diagnostics LEDs staying lit - these are labelled 1,2,3 and 4 and are near the front headphone sockets.
2) Does the LED on the power supply stay lit if you hold the power supply test button in/
3) Please remove all peripherals at the back of the system and switch the system on. Does this affect the power button LED or diagnostic LEDs?
4) Have you added any components to the system e.g. video cards, sound cards etc...
5) Please open the system and remove the following components:
a) Power and data cables from hard drives and optical drivesb) Any PCI/PCI-Express expansion cardsc) All memory from the systemd) The system fan
6) With the above removed, please reconnect the power cord to the back of the system and switch the system on. Please make a note of what happens with the power button LED and the diagnostic LEDs.
7) If there are no changes to the power button LED or diagnostic LEDs, please remove the power cord from the back of the system and remove the following components:
a) I/O panel cableb) CMOS battery
8) With the I/O panel cable and CMOS battery removed, please connect the power cord to the back of the system. The system should automatically try to switch on. Do you hear any beeps from the system? If so, can you tell us exactly what you hear?
If you need any assistance removing components, this manual will show you how to do so: <ADMIN NOTE: Broken link has been removed / replaced from this post by Dell>
Please let us know how you get on with the above steps.
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To help troubleshoot a problem, your computer has four lights labeled 1, 2, 3, and 4 on the front panel. When the computer starts normally, the lights flash before turning off. If the computer malfunctions, the sequence of the lights help to identify the problem.
The computer is in a normal off condition or a possible pre-BIOS failure has occurred.
The diagnostic lights are not lit after the computer successfully boots to the operating system.
A possible processor failure has occurred.
Memory modules are detected, but a memory failure has occurred.
A possible graphics card failure has occurred.
A possible floppy drive or hard drive failure has occurred.
Reseat all power and data cables.
A possible USB failure has occurred.
Reinstall all USB devices and check all cable connections.
No memory modules are detected.
Memory modules are detected, but a memory configuration or compatibility error has occurred.
A possible expansion card failure has occurred.
Another failure has occurred.
Your computer might emit a series of beeps during start-up if the monitor cannot display errors or problems. This series of beeps, called a beep code, identifies a problem. For example, beep code 1-3-1 (one possible beep code) consists of one beep, a burst of three beeps, and then one beep. This beep code tells you that the computer encountered a memory problem.
Reseating the memory modules may correct the following beep code errors. If the problem persists, contact Dell (see Contacting Dell) for instructions on obtaining technical assistance.
1-3-1 through 2-4-4
Memory not being properly identified or used
Memory failure above address 0FFFFh
If you experience any of the following beep code errors, see Contacting Dell for instructions on obtaining technical assistance.
Microprocessor register failure
NVRAM read/write failure
ROM BIOS checksum failure
Programmable interval timer failure
DMA initialization failure
DMA page register read/write failure
Video Memory Test failure
Slave DMA register failure
Master DMA register failure
Master interrupt mask register failure
Slave interrupt mask register failure
Interrupt vector loading failure
Keyboard Controller Test failure
NVRAM power loss
Invalid NVRAM configuration
Screen initialization failure
Screen retrace failure
Search for video ROM failure
No timer tick
Gate A20 failure
Unexpected interrupt in protected mode
Timer-chip counter 2 failure
Time-of-day clock stopped
Serial or parallel port test failure
Failure to decompress code to shadowed memory
Math-coprocessor test failure
Cache test failure
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1. The power button LED is yellow. Like I said, the power button only works if you hold the power supply button down first. However, if you hold the power button down alone it flashes yellow.
2.. Yes, it stays lit. It also stays lit after I turn it on the aforementioned way.
3. The only peripheral I had attached was a VGA cable to monitor output. Removing it does nothing.
4. The system is stock as far as I know.
5&6. Removing these still does not allow the computer to be turned on through the power button alone. I must hold the power supply button first and then press the on button. Still yellow LED power button, no diagnostic lights, and no video output.
7&8. I removed the CMOS battery. I wasn't sure what the I/O Panel Cable was, but I assumed it was component 8 described on page 5 of this link:
I plugged the power cable in and it did not try to turn on by itself, there was no beeping either. The power supply test button still works and turns the power supply LED green, however.
I think we've ruled it down to two components - either the motherboard itself or the PSU. Can I ask you to remove and reconnect all the power connections from the PSU to the motherboard? On some occasions, a loose connection can cause these problems.
I've also sent you a friend request so I can send you a private message - if you can add me as a friend and give me your service tag by private message, that would be a great help.
Tried reconnecting all motherboard connections, no dice. I don't think it's the power supply, forgot to mention that when I press the power supply test button all the fans go on, but I could be wrong.
In this situation, I think I would replace the motherboard. I would say, though, we haven't tried a different power cord. If you have one, I would try connecting the alternative power cord to the system, just to rule out that the power cord is causing this. Also, one other thing, are all the USB ports undamaged? I've seen damaged USB ports causing this issue.
Assuming that it's not the power cord and that there are no damaged USB ports, I think we can say that the motherboard has developed a fault here. Would you like me to find out the cost of a replacement motherboard for you? Please let me know.
I tried a different power cord, but same thing. However, one of the USB ports on the front (not on the motherboard) appears to be damaged. That's on the I/O panel, right? Could that be the issue?
Also, yes, please find out the cost of a replacement motherboard.
Tried a different I/O panel on a different Optiplex 755 on the broken one. Same problems. So I doubt the broken USB port on the bad 755 has anything to do with it. So it looks like we're down to the motherboard here.
You didnt say what the diag lights said.
You didnt say you tried ram 1 stick at a time.
If the ram is bad a new motherboard will not help.
If the video card is bad the onboard should still work with vga when the video card is removed.
If the power light is blinking amber — The computer is receiving electrical power, but an internal power problem may exist.
If the power light is steady amber — A device may be malfunctioning or incorrectly installed.
What I will say is that the broken USB port on the front I/O panel will require a replacement I/O panel for your system as well as a replacement motherboard - damaged USB ports can cause short circuits which can cause these problems.
I've sent you a private message - if you can reply, it would be very much appreciated.
Despite the working power supply test button, I tried replacing the power supply anyway just to see. Lo and behold, it worked! That button is a little liar. However, it appears that SATA ports 0, 1 and 2 are broken, and the BIOS only recognizes SATA3. So I need a new mobo anyway, on top of the power supply, and a new I/O panel it seems....yikes.
No one quoted my on the price for these parts that I need.
This forum is not Sales and Support. There will be no quotes here.
Amazon, Microcenter etc have the entire computer for $200 or less.