I just purchased a refurbished Dell Optiplex 745 with Windows 7 Pro. It came with a HP Windows 7 Pro re install disk and when I questioned them about this they stated that a HP re install disk is identical to a Dell disk. Is this true and if it is not what problems will it create if I have to re install Windows 7.
In that they are both Windows 7, whoever told you that is correct, but there are important differences too. Dell media is intended to be installed on a Dell computer and activate automatically, without the need for manual entry of Product Key. HP is designed to do the same thing ... on an HP machine. There is a good chance that it wouldn't accept the Dell Product Key either ... even if it did install successfully. Also, most OEM media will not even install on other than a matching machine (HP disks will not usually install on Dell, vice versa).
Also note that the Dell Optiplex 745 was never supplied with Windows 7. You cans ee on the Dell Drivers and Downloads Page that the drivers are only offered for 2000, XP or Vista (although Windows 7 runs perfectly on this machine using the Vista drivers, we have one in the office).
Is there any sticker on the side of the machine like this and if so what does it say (don't state the 25 product key). I mean does it say Dell, does it say HP, does it say Windows XP, Windows Vista or Windows 7.
Next can you read the 25 digit character key?
Windows Reinstallation Guide and Related Wikies See here for other wikies such as Customising and Using Windows 8.1, Dell Wireless Cards and Unofficial Drivers.
I haven't tried using OEM media on hardware other than that of its OEM, but I've had no trouble using OEM product keys with generic Windows 7 installs.
The only Windows 7 product key I've had trouble with was Family Pack; Family Pack keys can only be used with upgrades of existing installs, not clean installs. (And Windows can differentiate between the two.)