Odd are your system restore wont do it.
Your next step is going to be reformatting, and if that dont fix it look to your hardware you may have somthing failing. IE your powersupply.
Go to
www.trendmicro.com and use their virus scan as well. Housecall its called and it is completly free.
Sound more hardware related to me then anything though so Id check you Power supply, try reseating your ram (this could be bad as well.. Make sure when you buy ram if you buy more then 1 stick that it comes from the same batch never mix ram from diff companies)
Seenon