a power suply unit is were the mains wire connects to the PC case. the box is internal and will have multiple wires coming off it to power the mother board, graphics card and optical/hard drives (in some cases fans and lights). they are fairly easy to change as they are a contained unit generaly at the top of the tower. the only thing is you need to make sure you get with with enough of each type of conection so you can reconect it. also on the mother board there are generaly 2 socks and one can be either 4 or 8 pins and the other can be either 20 or 24 pins.

so if you feel you can understand enough how to disconect all the stuff inside the case and reconect it after getting the new power suply and make sure it is one that will fit all your needs it should be a fairly fast and easy change.

the only thing I will not is most nvidia cards only have 6 pin power conectors (not 8) and if you have sata drives make sure that you get a sata compatable power suply as they have differant power conectors to the old IDE drives.

also for a modern PC I would recormend atleast a 500watt to make sure it is more than you need as having more power than you need doesnt affect the PC but does allow it to take extra power if it needs to.

Ok. So I had this problem for a couple of days and I couldn't take it anymore. After so much searching around, and doing all sort of "fixes" I was on the verge on giving up, when I found a possible fix.
Currently I'm still trying to see if it works, so no promises.
I did some tests and here's what I found out caused it: (At least in my case)
-The problem is limited to certain games. I never had any problems with some games, while others crashed repeatedly.
-The crash occurs when the card overheats. (I opened my case, and put a big-*** fan on it, and no crash occurred even with games that kept crashing before.)

So from these two things, it is pretty obvious that the problem is not hardware related but rather driver related. (For me at least :S)
Now, most people would try to uninstall and reinstall their drivers, but would still have the same crashes. Some people even went to far as to reinstalling windows to solve the problem.
If you have tried to solve this problem by simply reinstalling windows over your current installation, then this wouldn't do much help, since reinstalling windows would only overwrite windows system files and not the nv4_disp.dll.
If you have already tried formatting your partition and still got the same problem, then the fix I'm going to give you will probably not work since it fixes the driver. (Also I think if doing this fix doesn't work out for you, then it would be useless to try formatting the drive since there would be like a 90% chance your problem is not driver related)

Now, as I have mentioned, even though to some people the problem is driver related, uninstalling the driver and then reinstalling it won't help.
The reason for that is, that the driver isn't completely uninstalled. Here is what I did to fix my problem(although I am still testing it and don't know if what I did only temporarily fixed the problem)
-First, download the 169.21 driver.
-Download and install driver cleaner pro from the following link: http://downloads.guru3d.com/download.php?det=745
-Uninstall the current Nvidia driver from Add/Remove Programs
-Restart your windows and go into safe mode.
-Run driver cleaner, and choose nvidia. This should pretty much clear all your old driver files which might have remained the same despite the normal reinstall.
-Install the driver again (preferably 169.21)

A couple of notes. If your AV program runs in safe mode don't forget to disable it.
And if windows driver install appears press cancel.
Also, if you keep having the crash try a last attempt at disabling your AV while playing.

As for the reason why this problem occurred in the first place, I noticed that a lot of people who have this problem had it after upgrading from a previous Nvidia card to a more recent ones, and I think that might be the reason why the driver got corrupted. Personally I upgraded from 6600LE to 8800GT so I guess I would fall into that category.

I really hope this would help most of you are having this crash. I'm still trying to test how things work for me, but so far I was able to play a hole level of devil may cry 4 at highest settings, while before I used to have this crash around mid-level, so I cannot promise that this would work.

You're running several drivers behind. You don't mention the OS, but both XP and Vista current WHQL is175.19 and that is already outdated by the improved 177.89 see here.

But your problem is most probably related to the fact that many if not most GF 88xx and 9xxx cards are sold "factory overclocked", which is a selling argument but makes the cards unstable in demanding games. The fix is to reduce the card's mem speed, you can use nforce system tools 6 for that.

You don't mention the other hardware/software components, but they are equally important for running a game correctly.

Like I said, this fix is in case the problem is driver related. There could be other reasons for it. I had tried uninstalling and reinstalling the drivers, but the problem persisted. However when I did what I described above, the problem was solved.

As for the outdated driver, even though 169.21 is a bit old, it is the one with the least problems. Not to mention that 175.19 are very buggy and many people recommend the 169.21 as the most stable one. Just search the nvidia forums and you will find people complaining about it.(like here http://forums.nvidia.com/index.php?showtopic=71645 ) I don't know about the other driver's though, as I am yet to test them, and quite honestly I am scared to try from fear that horrible BSOD will haunt me again XD. My current driver is working out great for me performance wise, and stable, and that's why I advised people to try it.

I'm on 177 drivers with a 8800GT and the game runs fine so as said above you will most likly find the problem is a conflict in something else that the driver causes to show.

I'm still getting blue screens with this error. I've tried everything from a format and reinstall to removing on of my vids cards from the pcf case to no avail. I don't own winxp, so I can't downgrade, and even if I could, the old OS couldn't run half my hardware. Does anyone have a solution that will let me play this game for longer than 13mins without a blue screen?

Sys specs:

intel q6600
2x XFX 8800GT Alpha Dogs in SLI, XFX Gamer Mobo,
6gb ddr2-800 ram (timing 4-4-3-4), win Vista x64.

my gues would be by the name of your graphics card it is factory overclocked and the game hates that use the nvidia system tools to clock it to standard speeds and it should clear up the problems.

Make sure you have SP1 installed, Vista64 SP1 has no problem with the game, also don't push your RAM overclock.
I'm running it with zero problems on HD4870X2 (stock speeds), and my 8 GB PC2 8500 RAM is at default 5-5-5-15.