Recently I did a bit of an overhaul on my old gaming computer, upgrading from an Nvidia 9600 GSO to a GTS 250, and overclocking the processor speed of the old Dual Core E2200 processor from the typical 2.4 to 3.2 GHz. Life was pretty good for a couple days, but then it started shutting down under heavy load. I couldn't have that, so I dropped the clock back down to the default 2.4. Everything was fine.
Eventually though, the motherboard and PSU failed, and I took the opportunity to upgrade with the rebuild. So now I've got a Phenom II x2 555BE on what seems to be a solid, if no-name board. The only parts that haven't been changed out are the graphics card (my beloved GTS 250), and the RAM sticks (corsair 5-5-5-12 sticks at 1.8 volts). The temps have been good, the computer is blazing fast compared to what it used to be -- and it shuts off under load again! So what do you think, Tom's? Time to test the old video card out and run some tests on the RAM? Maybe increase voltages a little? I'm writing this as I go to bed, but I'll be sure to respond in the morning when I've had some time to sleep.
Edit: I thought I should mention that I'm still running the same programs I ran with the E2200: TF2, Heroes of Newerth, a couple other simple games, and then the big boys, STALKER: Call of Pripyat (complete mod) and the Crysis 2 multiplayer demo. Both of the latter two crash within 20 minutes of play (if that), and are intensive on all parts of the rig. I mostly suspect the GPU because TF2 can be reasonably demanding on the processor, but significantly less so on the GPU, and has never given me a crash like this, whereas Half-life 2 has in SPOILER the infamous G-Man scenes.
Second Edit: System specs
AMD Phenom II X2 555BE processor
2 2 gig sticks of Corsair 5-5-5-12 RAM
Nvidia GTS 250 gpu
Logisys PSU, stable at 450W. Part # PS575XBK
abit N11360 mobo
Western Digital 5000AAKS HD
Don't increase the voltage; that just produces more heat. You may have a heat issue with the video card, but that's just speculation. I tried unplugging my tiny but noisy fan on a lowly 210 card, and the screen went blank after 5 minutes from heat. Plugging the fan back in fixed it. I hate noise.
What PSU are you currently running? Sudden shut downs under load are often the PSU getting overloaded or overheating and cutting out to protect itself. List your current system specs as that gives us a lot more to work off of.
Also, when stuff like Stalker and Crysis 2 demo crash out, does the system just turn off, or does it lock up and require a restart, or does it cut to a BSOD?
Found your problem. Its 12V rail only has 25A available, your graphics and your CPU both pull ALL of their power from the 12V rail and you only have 300W available for them and the rest of the system to use, the GTS 250 uses 150W under load, the 555 will use about 95W, which only leaves about 55W to spread between the drives, the fans, and the motherboard components, that not much and that assumes that it can actually give you every last bit of what it claims(unlikely from the looks of it). Looking at the load table you can tell its an older style unit as much of its power is on the 5V and 3.3V rails, it was slightly modified to allow it to work with ATX 12V style boards but it wasnt designed to do it from the start, its just too weak to support a system like that.
Yeah it will do fine, they balance which connectors are on which rails so that you dont have multiple power hungry things sharing a single rail and causing it to shut down, and the combined power behind those rails is more than enough for a GTS 250, its got a lot more than your old unit did.