Overclocking X1900XT in CSS reboots my PC

[!TIMMY!]

I have a Sapphire Radeon X1900XT 256mb PCI-E, and if I overclock it then my PC will reboot in CSS, but nothing else. Even if i overclock by the smallest amount possible. I have had it running at XTX speeds and it will run BF2, 3DMARK05/06 and AquaMark fine. It just in CSS that it reboots.

I get no artifacts in BF2, 3DMARK05/06 AquaMark and ATITool 0.26. But I did once in CSS just before it rebooted.

Temp is not an issue, i have a arctic cooling Accelero X2, and i monitor my temps with Rivatuner. My load temp at stock is around 70C and at XTX speeds is 80C. So what could be causing my PC to reboot?

I thought my Hiper 580W Type R PSU, because i thought i only had 1 12v 18A rail, but i found out that I have 2 12v (1 20A, 1 18A) rails in here, so I don't think it would be limiting my graphics card oc, would it?

I have the graphics card on its own PCI-E power cable with nothing else attached to it.

Can anyone shead some light onto this, google hasnt really help so far

 

[Hyper]

Sounds more software related than hardware because if it was due to too much of an overclock then no games would run.

Are all your settings set to default in CSS, try lowering them a bit and trying again.

Seems a little odd though how it only does it in CSS

 

[jiffz]

How long can you play for before a reboot? Also, have you tried different drivers + what do ya use to overclock?

 

[!TIMMY!]

1. Anywhere between 15-45 minutes.

2. Ive only used the latest offical ATI drivers, and ive tried re intalling them (with driver cleaner pro).

3. Ive used the ATI drivers and Rivatuner to overclock.

Ive used highest settings in css and lowed AA and AF, but still makes no difference.