I built a PC in December of 09 and it's been running great. Last night, though, it turned itself off a couple of times during use (twice in a three-hour period). Then this morning when I went to turn it on, it showed the Gigabyte screen before going to a blank black screen with a flashing line in the top left (like when you're typing). It wouldn't go past this screen.
I tried turning it off and then on again, and this time it went to the next screen for a split-second before showing the same empty black screen.
I did put in 4gb of RAM last Saturday, but the computer has been operating just fine since. The only other thing I can think of is that I downloaded AMD Overdrive to attempt OC'ing my CPU for the first time...but I decided not to OC when I saw that my cores' temps were already operating at 46C shortly after start up with no other programs running and about a minute into Autoclock they were at a sweltering 75C. I cancelled the autoclock immediately and haven't messed with Overdrive since, but now I'm thinking I probably fried my cpu.
Any thoughts/ideas? Preferably one that isn't as expensive as a new CPU?
If I had to guess - I think you got a bad stick or RAM. Especially since you mentioned you added some new RAM last Saturday. If you got a pair of RAM sticks - take one out and test your machine with 1 stick. if it's still bugging out - Swap out the RAM for the one you took out and try to boot with the other Stick. And check your MOBO manual - so you put it in channel 1 if you'll be the single channel in the proper slot.
When I had a stick of DDR Ram go out on a dell a few years ago - it caused all kinds of random shut downs - and not able to power up similar to what you're describing.