Help Pc keeps locking up in game.

[Roeg1]

For some reason of late My pc seems to be locking up, for the sake of me I cant work out why. Im getting this mainly in l4d if i alt tab out and then back in it will unlock for a second or two and then relock, everyone else is getting on with there game so its not the server.

Here are my bios settings only things I've changed of late are aftermarket cooler for my gpu and some corsair xms pc6400 that was on offer on ocuk few months back.

My core is only at 3ghz and as been stable for about 12 months. Ive ran ITB it passes 5 loops easily on standard stress times to run 5 threads on auto if i change it to 4 thread which i guess you should for a quad and max test it gets to the second run and comes up with critical error. Ran prime for an hour or two and that seems fine.

Here are my main bios settings.
external clock: 334mhz
multi:9
ram speed: 1:1:20 (ddr-2 801)

Dram setting : BY SPD *stuck all these on auto still the same*
vcore:1.3275
ddr2 volts: 2.1000
cpu VTT1.2volt: 1.20
MCH 1.25v : 1.37
ICH: 1.05
ICHI0 :1.5v
ddr2 refrence vots: 0%
CPU GTLREF 1/2: 67%
CPU GTLREF 3/4:67%

Any other info needed ?

 

[Roeg1]

answer to the two questions

1. FSB is ar 333mhz i believe multi at 9 so that = the 3ghz im at.
2. Abit ip35pro

as vortex i get these issues also.

I have also had problems when booting my PC, it will sometimes say it can't find the HDD, i turn off the power to the computer, turn it on again, and lo behold it works fine.

The computer behaves as if something is overheating... yet some days it will have been turned on pretty much all day and run fine, yet other days its on for 30mins and it plays up so it can't be a heat problem.

strange to say the least.