Don't really know too much about this kinda thing mate but the crashing/screen going onto stand by mode and not recovering, happened to me a while back and my graphics card supernova'd, seemed to happen more and more frequently till it eventually went kaput and had to replace the card, hope it's a much more simpler problem than that though.

Maybe you have a virus or a botnet (check here: http://www.botnetchecker.com).Other than that your probably putting too much strain on your pc try defragmenting your disk and registry or something.

Yeah it could be your power supply or whatever...I don't know much about hardware. I had a ps3 that would always crash I kept playing it and it ended up dying so I'd be careful.

If you are using vista you could be running low on ram. could try going back to xp or upgrading ram. If you never had these probs before and you are getting them now then i reckon something is about to pack up on you, prob the most expensive parts! Keep an exterior fan blowing on the pc, lower resolution and miminize the programs using ram if you can. failing that you could get a cheap laptop for one set of applications and save your main pc for gaming... Personally I can only see this getting worse and my guess is that it's the motherboard that's knackered (but i hope i am wrong actually) ! Also you could try something like tune up utilities to optimize the pc. I have some serials for it so if you are interested let me know(im on facebook too)

jaywhite1972@yahoo.co.uk

How's about running all your usual things with the system manager open?

This way you can see your system memory useage. If you peak at 100% for any extended amount of time, that could be your crashing issue.

You could also open the case and clean it out. If it is an overheating problem, just doing that can help immensely.