Windows XP 64-bit crashing

Hey guys i signed up to this forum because I'm desperate for help. I've had this comp for the last 2 years and its never had any problem this big, but suddenly today its started crashing at random times, so often that i can't even use it. I don't know much about computers but the basic speccs are:

Windows XP x64 bit
Quad core
4gb ram
nvidia geforce 8800 gt

Sometimes it can crash while I'm still starting up the computer, but at other times i can start it up and it'll only crash when i turn on a heavy program, eg: a game.

90% of the times when it crashes, it has these strange blue dots across the screen, if thats relevant.

Oh, and also when it crashes it stops making any noises (i mean the humming-ish sounds from the comp stop). The screen just freezes, ctrl alt delete doesnt work or anything (occasionally though i can move my mouse, but clicking doesnt work).

It COULD be a virus i guess, because my anti virus expired 2 or 3 months ago and i haven't replaced it... just trying to give you guys as much info as i can.

I tried using CCleaner to clean the registry and everything, but that didn't help as far as i could see.

Please help asap guys!!

EDIT: Final note, the thing thats strangest about how it crashes when i turn on a game, is that usually i can have Limewire, Mozilla firefox and about 2 or 3 games on AT A TIME without it crashing. Now even having mozilla and 1 game on can crash it (and thats if i'm lucky).
 
The 'blue dots' phenomenon may means that it is the issue with your Graphic card.

Do you see a blue screen at any time ? If so please attach minidumps for analysis with your next post, you can find them in C:\windows\minidump. If there are multiple files please zip them together.

If there are no BSODs involved here, you can go to Control Panel, Administrative Tools, and to Event Viewer, check logs thoroughly to see whether something useful is being recorded for these events.

Lastly you should stress test your GPU with OCCT to determine whether it really is the culprit here. Regards
 
OK new development: Now when i try to turn on my comp, it crashes before the login screen so i can't get on to try those things :( . I'm on my dads laptop atm.



EDIT: I just read that dust and dirt can cause these crashes also. What are the chances that my problem is caused by something like that? I haven't opened up my comp and dusted it in about..... ever. lol I was always afraid of messing something up.
 
I can't clean the inside of my PC till later on today or tomorrow but I'm starting to think that the problem IS with my graphics card.... Every single time before it crashes/freezes/ completely locks up, something happens to the colours on the screen. Right now, it crashes 90% of the time on the windows loading screen when starting up my comp and when that happens, sometimes the loading bar / parts around it can change colour to yellow or red before the PC just locks up.

I just tried in vain to change the main power cable to a fresh one (had a spare) but that didn't help at all, so I'm not sure if the problem is power related.

I haven't seen any blue screens yet though, as far as I can tell.
 
If you have an integrated graphics card, use that for the time being and see if the crashes still happen.
If not try booting into safe mode.

EDIT:
Windows XP x64 bit
Or it might just be that, since it hates everything.
 
No it doesn't Kitty, I used XP x64 for the better part of this decade till Vista x64 and later on Win7 x64 came along. Over the years I've used different graphic cards with these x64 OSes and none have every given me issues, unless it was hardware which was at fault. And my first thought and suggestion to OP was the same, having said that, I think if he has onboard VGA or can borrow a graphic card from a friend, perhaps he can check this theory out.
 
Hey guys, I'm too inexperienced to try opening and replacing the graphics card but I cleaned the PC out - paying special attention to the graphics card - and it didn't do much (in fact it may have made it worse). So I'm gonna take it to a shop to get it examined / fixed. If I have to replace this graphics card (nvidia geforce 8800 GT), what can i get for around $100-120 thats at least as powerful (if not more so)? I want this for gaming btw!
 
If you can bump that range upto 140 or so, you can get Radeon HD 4870, which is still a very very decent solution.

However, if you want to stay in your range then you may consider having a look at Radeon HD4850, or a Geforce 250 GTS.
 
Hmm, is the 4870 that much better than the 4850 to be worth the extra cash? Cause if the difference is small, then I might just go for the 4850 - I'm gonna be paying enough to get it fixed after all. And out of the 250 GTS and the Radeon HD 4850 which would you choose? I've ALWAYS used Nvidia before so I'm a bit hesitant to pick ATI over it, but I've heard good things about it. (Oh, and both of them are better than the 8800 GT right? :S )
 
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