Cannot choose mac partion in startup manager. Option Key not working. Bootcamp chaos!

Hey guys, I've done a really retarded thing so I guess I deserve this....

I wanted to get XP service pack 2 on my imac, so I started up bootcamp and unearthed a copy of windows I owned for my old Dell. Apparently, this disk was only for REinstalliton of XP, but I used it.
Anyway, I started up bootcamp and put this disk in, The screen went black and the computer automatically rebooted into the windows partition, only the windows partition was all white writing about system 32 corrupt and all that. Ah well.
I turned the computer off by the power switch and held down the option key at start up so I could choose my mac partition. I got into my mac partition and everything was fine.
however , the next day, I held down option key in start up again and suddenly the keyboard is totally unresponsive! No keys are working! Now the computer only boots up in the totally useless "Windows" partion!
I cant boot from disk or anything.
Please help me! and thanks

and yes the keyboards working, plugged in ect ect i even tried a different keyboard.

Also, I've been turning the computer off by the power switch quite alot because it's the only way I can get back to the start up manager. Is this hurting my computer?