Windows XP Pro and 1Gb of ram?

Ok I have win xp pro and i had 2-256Mb chips and everything was fine. I went and got 2-512Mb sdram chips and now i get random restarts.

PIII 800EB
AOpen AX63Pro Motherboard
PNY Verto Geforces3 TI200
HP 12x10x40x Burner
Creative SoundBlaster??
RK-byte 512Mb 2ea. SDRAM PC133
TV tuner Pennacl(or however it is spelled)
Eithernet card
PCI ata133 card promise
80Gb ata133 HDD


Like I said it randomly reboots. Can't run SISANDRA Burnin without it rebooting after a few hours. 3DMARK2001 will not run all the way through the benchmark anymore. There has got to be some setting I have missed some where! IE6 will crash every now and then too. I was reading somewhere that there may be a cache setting in the reg i have to change. But I have no clue on this one.....HELP!!!!!

sounds like bad memory, try one stick at a time and see if one restarts and the other doesn't.

Memtest, docmem, etc suck!!!!!!!!!!!!!!

I mean really!!!! The test showed both were good. Checked both chips using the old game the hell outta it and crashed....put one at a time in and whola! One is bad...go figure why those mem tests showed good? Thanks!