Hello there. I bought computer around 5 years or so ago (Alienware Aurora R4 ALX, with a GTX 690 and an i73960X). I've had issues with it this past year where The monitor would turn itself off (and say no signal) particularly under heavy load, and I'd have to restart it a few times in order to stop the monitor from going off. Sometimes the PC would turn itself off after a while, but most of the time I had to do so via the power button. So as I said, after a few restarts it became stable, and there were no issues in its use. However, the past few weeks it's been occurring much more often and the performance once it is on is terrible.
I usually have a stable 100fps or so while playing World of Warcraft, and that's in densely populated areas. However, the last few weeks my Dow has been dipping constantly from 100 to about 24 fps, even in low populated areas and places with lower graphical content.
Now, I turned my computer on this morning and it will now no longer go past the windows startup logo. Once the logo has appeared and it goes to load, the screen turns to a white-like colour with bars and I am unable to do anything from there.
A short while ago I'd also sometimes get a BSOD with the error of Attempted execute of non execute memory, though this was quite rare.
Update: I did as suggested above, removed a RAM module at a time (I have 4x 4GB) and the whitescreen remained until the final one. In order to check it wasn't specifically the last one, I switched it out with one of the RAMs I had taken out before it. This time, however, my PC turns on, but the screen isn't loading at all, not even getting a signal lost or reaching the bios. The RAM is in correctly and I don't think it's the MB as that was beeping when I accidentally hit the power button when I had no RAM in there. But as I said, now it's not even turning the monitor on, though the PC and my RGB lights/fans are working.