Very weird computer shut down/black screen/boot problem...help, please!
It started with a random shut down while I was surfing the net. OK...I rebooted, and got back on. Well, it didn't shut down, but the screen went blank and I couldn't do anything, So, I did a hard shutdown, and left it overnight. The next day I brought it back up in safe mode. Well, within a minute it went blank again, and I had to do a hard shutdown. So, at this point, I am thinking it is not a thermal problem (??). So, I try starting it back up...and I get nothing on the screen (no boot screen, nothing at all), and something is spinning up, then down, then up, then down... Hard shutdown, and try again. This time it sounds like it is booting OK, but black screen. So, I disconnect my video card and plug into onboard graphics and try again. Booting, but nothing on the screen. I try again, and it boots and I have video. I run diagnostics from the boot screen, and it says "MATS test pass, March B test pass", but nothing else happens. I reboot, and go into safe mode, and try running a malware scan, and it flashes a BSD for half a second, then no video. Reboot into safe mode, and now it seems to be staying up.
EDIT: It just lost video again after about 15 minutes...running on onboard graphics. The monitor is showing a signal input, but it is black screen. When it boots without video, there isn't even any input...the monitor remains on standby mode.
I am at a total loss...can anyone help?
I have an Radeon HD 5670 running with only a 300W PSU...not the best idea, but it is a super low power draw and has run fine for almost a year. I haven't pushed the card at all. Otherwise, it is basically stock - Athlon X2 Quad Core 630, 6MB RAM, 1 TB HD.