'BSOD' Crashes While Playing Games

Since purchasing my computer a couple of years ago, I have been afflicted with random 'BSOD' crashes. At the outset, they would occur whenever I ran anything intensive (a three-dimensional game, for example). I was told the problem was likely a lack of/bad RAM, so I purchased more. For a while, all was well, until the crashes began occuring again (a myriad, really: IRQL_NOT_LESS_OR_EQUAL, PAGE_FAULT_IN_NONPAGED_AREA, etc.) some months later. Not possessing any vast knowledge of computers, I again purchased new RAM. The problems seemed to subside, though occured still occassionally (no rhyme nor reason).