oldbeans

hi all just a quick question

i recent baught 4 gig of corsair xms2 ddr2 800 for my PC (2x2gig) befor this i was using veritech ddr2 533 (2x1gig)

befor i baught this i hade oc'd my amd athlon 64 x2 4200+ (2.2gig) to run smoothly at 2.7gig

after buying the ram taking out the old ram and sloting in the new ram i noticed my bios had been reset and my cpu was back to stock standed

ive tryed a few times getting my cpu back to its oc'd state of 2.7gig but each time results in pc not booting (power runs, fans start but no POST beep and im left with a blank screan)

my pc specs are

abit kn9 mobo
phoenix bios version 6.00 pg
amd athlon 64 x2 4200+
corsair xms2 ddr2 800 (2x2gig)
geforce 8800 gtx
antech truepower 2.0 550w output

any advice on what to do would be greatly apreciated