Computer wouldnt boot, now it does. bad sign?

Hi,

I have an old computer I bought from Alienware over 2 years ago and out of warranty now, I had problems ever since I bought it with the computer freezing and locking up. Alienware replaced the motherboard once, the graphics cards and the RAM over the course of the first year but i still had the problems, the latest RAM they sent me failed memtest at which point my warranty ran out and I just gave up.

now, a year later, I bought some new RAM and left it overnight using memtest. It passsed, however i have still had some strange issues since then.

- my screen went blank then returned and I got a Display driver is not responding and has recovered message
- at one point i got what i belive to be a PSOD first and last time i saw that was just after installing the new RAM
- computer acts really sluggish sometimes, even after doing a clean install
- really bad screen tearing while playing C&C, only lasted about 20 secs and not seen it since

The most worrying...

- last night the computer would not boot AT ALL, i have a 790i ultra MOBO and when i looked inside it's blue LED was on when the computer was plugged in, the orange LED would turn on when i pushed the power button and i could hear a very quiet slight buzzing from the back of the power supply.

I assumed PSU had died and was planning to buy a new one this morning, however now it suddenly works again, since last night I did take one stick of RAM out but i dont think this is what is making it work. (i also tried with one stick last night and it wouldnt boot)

when i ran memtest overnight it was the longest my computer had been left on since i got it, must have been around 35 hours it was on.


Am i right in thinking this is a PSU issue, or could something else be dying?