Keyboard failure

I have a Dell dimension 9150 with dell keyboard and dell mouse (both USB).
My problem is that a couple of days ago I was playing my computer when it suddenly froze. I shut down the computer and turned it on again. Now when it is booting it stops for a while on the first Dell screen. After 20 seconds it moves on but writes: "Keyboard Failure".
The result of this is that i can neither use my keyboard nor my mouse which indicates that i am rather stuck!!!
I can't press the f1, f2 og f12 bottons.
I have tried to use the other USB-entries.
Both the keyboard and the mouse works perfectly on my laptop.
Can anyone please help me?