Firstly:
* Sorry for my "english" (I'm from Poland)
* I was looking everywhere for solution for my problem, but I didn't find it, so I made a new thread, sorry if there was a solution and I did not find it (then please give me a link)

So, let's begin.
I have a big problem with games. I can run them, but after few (5 -10) minutes BSOD shows up and my computer restarts. It concern all games I've tried to play, so I'm sure there is no problem with these games. I have a really good computer, so all of these games should work with the best settings. I've also tried to run them on my friend's computer (his machine is much older then mine and it has worse hardware) and everything was fine. I don't know how to solve this problem, so I ask for Your help.

That's my computer:
* Intel Core 2 Duo CPU 2.66 GHz (2 CPU's)
* 4096 MB RAM (dxdiag displays 3328 MB RAM)
* Windows XP Home Edition SP1
* DirectX 9.0c (from march 2008)
* NVIDIA GeForce 8600 GTS (256 MB)
* PSU 400 W

I was trying a lot of things like reinstalling system, defragmenting, searching for viruses or bots and there is no positive results.
Please help!

STOP: 0x0000008E (0x80000003, 0xB624BB74, 0xF78A2c40, 0x00000000)
RtkHDAud.sys - Address B624BB74 base at B61AB000 Date Stamp 4607ac8c

A stop error(BSOD)can be caused by software, but is most often a hardware issue... more specifically faulty ram. I suggest that you download memtest86+ and test your ram. Download the ISO(link at bottom)unzip it to the desktop, burn the ISO as an image to a CD and then boot from it. If you get even a single error then you will need to replace some ram. If you get an error(s)you should then test the sticks 1 at a time to isolate the faulty stick(s).

Download the ISO from here:

http://www.memtest86.com/memtest86-3.4a.iso.zip

On a side note: 400w is a bit wimpy, if it's a good brand/model with sufficient amps(no less than 30 will do IMO)it should be enough to scrape by. The bottom line is that I'd recommend getting at least a 500w PSU with at least 40 amps on the 12v rail(s).
It's possible that your problem stems from insufficient power, but I still recommend testing your ram.

BTW: Your english is just fine!

You have right, there were some problems with ram.
I've remove the faulty ram and everything is alright now!
Thank You very much!

I'm glad I was able to help and that your system works as it should now!