Random crashing with all games

Hello, recently (last month) I received a major computer upgrade which I played with eagerly for about four weeks, with no crashing or any problem of any kind. But after those four weeks, things started going weird.

All of my games now crash at one point or another, at random intervals. For example, sometimes Fallout 3 crashes when I enter V.A.T.S, sometimes when I load a new area. Or Half-Life 2: Episode One crashing when I load the next area, or fire a gun. What happens afterwards seems to be random too, occasionally going to a black screen and requiring a restart, occasionally simply crashing to desktop, and occasionally messing up the graphics scheme (setting the display options to 4 bit, 640x480). The games run as perfect as when I got them and when they were not crashing, and I see no visual artifacts or frame rate drops. Before the problem I had overclocked my card slightly, with no problems and no overheating. I have since turned down the clocks to the defaults, but to no avail.

One other thing to note that may or may not be related, is the fact that the day my games started screwing up I upgraded four different components of my computer with drivers from an automatic driver finding program. Two of the components were nothing to do performance wise (mouse and monitor drivers) but the other two included an Intel Chipset upgrade, and a 'Marvell 61xx SATA RAID controller driver'. I would like some clarification on what exactly I upgraded.

My system is:

Processor: Intel Core 2 Duo E7400 @ 2.80Ghz
RAM: Kingston 2x1GB DDR2
Graphics: ATI HD4870 512mb (says 1GB everywhere else though)
Motherboard: ASUS P5Q SE/R

Since this system is brand new, I would not like helpful messages like 'ur mobo is dying'. If any part is, indeed, dying, please provide a credible explanation on why it would be happening.

Oh sorry, my power supply is an ATX 530w.

generic psu? there rubbish - replace it with a branded ~550+w psu