[help] Keyboard and mouse suddenly not working

-My usb keyboard and mouse suddenly don't work after I switched out a dvd drive.

I know the keyboard and mouse work, as I tested it out on another computer.

-I can't get either the keyboard or the mouse to work in safe mode either.

-When I boot up the computer the keyboard works to select the various options, but when it goes into Windows XP it doesn't work anymore.

Not sure what has gone wrong.

Help!

 

hmm, I thought USB devices could be plugged into any inputs? Is this not the case?

 

thx, it seems to be working now..

but still didn't know that USB devices had specific inputs that needed to be plugged into.