My computer keeps restarting itself

hi
i seem to be having problems with my computer. basically what is happening is every so often my computer seems to restart itself the first few times it happened whilst printing. but after that it started doing it at random times.

i did run a spyware check using spyware blaster that found quite a bit of spyware which i got rid of. apart from a few others which were in the registry keys which i didnt delete because i wasn't sure wether they were important or not.

i would be very thankful if you could help

thankyou
nadeem