Try the Dell Repair your computer and see if that fixes it. I don't think it will delete any user data, but I can't be sure as I don't have this on my Dell.
Press F8 at power on and that will access the Dell Recovery Partition. Of of the options should be repair your computer.
If you can access Startup Repair by pressing F8 before Windoew starts (different than the Dell Recovery), you can try to fix it that way. The other way is to run startup repair from a Disc. You can download Windows 7 (download the exact same version of Windows 7 you have - such as Home 64 bit), create an iso DVD and use that for the Startup Repair.
If Startup Repair will not work, you are looking at a complete reinstall.
Windows 7 download
Imgburn (CD/DVD burning program that wil burn an iso DVD)
How to run Windows 7 Startup Repair
I am not a Dell Employee
Dell forum member since 2002
Inspiron 15 - 5577 Laptop
Home Built Desktop PC with ASUS Z170, i7 6700K CPU, Windows 10 64 bit Pro. SSD drive. Sonar Platinum Recordng Software.
Member of Nashville based R.O.P.E.