Vista - keeps crashing

my friend has an alienware comp and it keeps crashing he is running the asus p5 and unfortunatly his warranty has expired it's also running xp it will crash from boot or some times after 10min other times it's after a few hours.

he is running a 7800gtx 256mb gpu also, if anyone knows of any fauts this has after 2 years of use would be appreciated i am recommending a new card for him too 9800gt or there abouts something usefull but not overly pricey as he doesn't require it for things like crysis and stuff

i'm looking for things to look for to help him resolve it as the alienware call out charge for him is 600quid i told him to just get a new comp but he would like to keep it for a while i'm going to fit new ram that i have lying around as i think it may be a hardware fault as there is a strange noise coming from his computer possibly making it an overheating issue but when i googled his comp i got a ton of hits on the same fault with the same comp so it's not a one off case and nowhere was there a solution so i figured i'd put to the people who know how to help.

thanks to all who offer tips or advice

ps. the ram is just cause i can and i'm just going to exhaust all available options first so don't ask me why i'm doing that.

Open the machine, turn it on and find out from where exactly, "that strange noise" is coming from.

Both HD and PSU would make strange sound when going out. Besides check on this two, I would first make sure if the CPU hsf is free off dust and the thermal paste is still fresh. Blow out the whole inside and make sure all connections are all good. See what happens and start from there.

You could run Memtest to test the RAM, but if the machine is crashing frequently, it may go down before the test is done...Faulty PSU's can do this....Have you got one to swap out? run the machine with the case open...how hot is it getting?? try to locate the sound.. but that really may not be reliable as I had a PSU going bad and it would surge before causing a crash, the surge would wreak havoc on the Video card, video card fan, HDD drives..so sound may lead you in a direction at least...but can be hard to really know for sure whats the cause...got a card to swap out? I know only too well how difficult it can be to be positive about a failing Graphics card..put the machine through some hoops ( play some games...run apps..got any folding programs?? If so run it.) and pay attention to when it locks up..this may help get a better idea of whats starting the problem. Bruce has the right idea.. start with connections...clean any really bad dust, look for overheating problems...test or run hardware...run apps...all paying close attention to when it locks up. If your handy with a multimeter, ( and I mean really handy..with knowledge ) you could check your PSU while its running...but if you have one to swap...you could do that. The memory swap is good too.. but you may find swapping out could cause some issues and now not know for sure which problem is from what..Aliens are very touchy... I've had two...both were very quirky with hardware. Good luck and please let us know...someone will benefit...

ok an update on this i found why it was crashing i ran some tests to stress the components after i replaced the ram with newer stuff ocz ddr 2 800 sli which gave a nice performance boost anyway during the tests something caught my eye the cpu tem on idle was 63deg c which i thought was oddly high i checked the safe temps from intel and it cuts out at 68deg c so from idle to load it had 5 degres to play with!
as it turned out although the cpu fan was running it wasn't cooling the cpu enough if at all a quick change of that fan and heatsink saw the temp drop to 35-45deg during use and the annoying noise go too, in light of this i recomended a new cpu as the ammount of times it crashed may have damaged it or certainly reduced it's life. he is also upgrading to a 9800gt 512 oddly cheap from pc world at £98 compared to newegg and lambdateck so pc world not bad for everything lol, to bring his system up to date he wants to be able to run dx10 games but i'm fairly certain they only run in vista and not xp at least in dx10 mode although they will run in dx9 on both os's.

well another system problem solved by the might of the great minds on this forum.