Vista Stopped Recognizing Kb/M Suddenly

Yesterday I reinstalled Windows XP Media Center Edition on my Vista PC(my old install of XP was getting kinda slow- too much junk installed). After putting the Vista boot CD back in after install to fix the startup menu(installing XP overwrites it and removes the option to boot into Vista), I found that Vista no longer recognizes my keyboard and mouse, so I can't log in or do anything.

I've tried reconnecting all of my USB devices, and plugging them into different USB slots(motherboard and on the USB cards) and nothing makes a difference. Booting into safe mode didn't help, either. I have also tried using a different keyboard, but Vista didn't recognize it either.

I can tell power is going to my keyboard because the backlight is on.

Any suggestions on how to get Vista to recognize my keyboard and mouse again?

 

Also, I tried plugging the keyboard/mouse in via PS/2, and it still didn't work. I need to get this fixed fairly soon. Help?