Problem with K7V Dragon+

[DoubleL]

I have a problem I can't seem to find, I had it on the bench at a computer shop and everything tested out ok, If you run the computer with no programs it will run 3DMark all day but that is at nomal bios and cas 2.5 if you change it to turbo and cas 2 it will not boot up, After you add your programs even at normal bios and cas 2,5 it has problem and lock ups, I have run this computer for close to a year at turbo, cas2 with no problems, It showed no signs of anything just started with the problems.

Enermax 431 watt powersupply
XP1900 processor-
Swiftech MC462A -
Asus 8200 GF3-
SoundBlaster Audigy-
Maxtor D740X Ultra 133 not running raid
Two sticks 256 Corsair 2400 cas2-