If yes, then try switching the USB plug to a different jack in the back of the computer..
Tried changing the batteries on the mouse and keyboard?
If that doesn't help, have you recently changed a setting in the BIOS regarding the USB "Legacy Support". It can frequently make a difference if you disable such.. Make sure it's enabled there.
Of course, using a PS2 mouse and keyboard should stop the problem you're seeing...
Hope this helps.
Ok so this problem started on Saturday. I was doing work on Friday my computer worked fine that night. then i turned on my computer Saturday morning and it was giving me a problem. The problem being when i got into the password screen my keyboard and mouse would not work no matter what. It works just fine in the bios but will not work once windows boots up. Will upload video explaining my problem when youtube stops screwing up.
Dell Studio xps 9100
Radeon HD 6870
9GB DDR3 Ram
525w Power Supply