pc acting on its own

Hi folks , hope you folks can help me out been a while since i been here ,lot a help last time round ...k here goes .pc can run smooth as ..then goes awol like says key board acting up or looses my second hard drive keyboard if hit delete opens anuther tab ,hence while typing this dun it a few times ..lol.can run fine for ages then decides to act up dunno if down to old age memory or infection . help is required if you guys can take yer time out to help me on this one wud be a great christmas prezy meny thanx