How do I get XP to detect my mouse/keyboard?

Hi, thanks for your attention to my question.
I recently bought a new PC, and rather than transferring all my files manually, I simply moved my old hard drive into the new computer. The OSes (I dual-boot XP and Server 2008 R2) boot fine, but XP will not detect my mouse and keyboard at the login screen. The mouse and keyboard both have power; XP simply does not respond to my clicks/keystrokes. I tried plugging in a PS/2 keyboard but that doesn’t work either. XP just refuses to recognize any input devices.
It’d be a real shame if I had to reinstall just because my keyboard/mouse weren’t recognized… is there a way to fix this problem without logging into XP?

Thanks!