New system. Computer either moves in slowmotion/reboots

So, I bought myself a new setup maybe 10 days ago or so and been having some problems right from the start.

It started out with me installing Win XP 64bit, when it was done and all the drivers were installed, every now and then (maybe every 5th och 6th startup) the computer reboot itself when going from the "windows loading" to the desktop, showing a quick blue screen the second before. It also reboot itself unannounced when just surfin the internet/doin ordinary stuff a few 2-3 times in windows during this first week or so.
Anyway. I was trying out different graphic drivers and such but couldn't get it to work, so I thought I might install Win XP 32bit and try it there. Same thing, just without the blue screen, it goes dark and reboots when entering desktop. So, I started trouble shooting the hardware:

Memory:

-Tried running it one by one.
-Tried changing the memory modules
-Scanned the original modules with memtest86

No changes, and the test said they were just fine.

Graphic:

-Tried changing drivers
-Tried changing the graphic card
-Tried both inputs on the motherboard
-Ran some benchmarks just for stabilitycheck and it seems to work fine

The problem was still there.

Storage:

-Ran both the SSD (systemdisc) and other SATA through HD tune pro and Seagate tools for windows, and they both passed.

I have not yet run themselves as systemdiscs one by one.. which might be the next thing on the list, I guess?

So after this I was pretty confused. I tried starting windows in safe mode maybe 10 times or so just to see if it reboot itself there too. It did not, which made me to believe the problem had to do with drivers. I reinstalled Win xp 32bit and went with new drivers to everything, installing every driver one by one and after every single hardware driver was installed I tried rebooting 7 times just to see if it reboots when entering windows. They all passed.. and I thought, Great, the problem is solved! Nono. There are new problems. For some reason, on occasion, the computer starts movin in slowmotion just when surfin or chattin or whatever. The mousepointer disappears, but u can still write although it lags.. and you will have to reboot to get it workin again.
Also. I tried installing far cry 2. There, it either closes down the game without further complications, or the computer just reboots while playing.
Once again.. I tried different graphic cards with the game, the same thing happens. One other problem too. Sometimes when I either view a clip in the flash player/youtube in fullscreen mode, the picture freezes with the sound working fine, forcing you to minimize (where it always works fine) and then go to fullscreen again for it to work.. but then seconds later it could happen again. I tried different codecs, did not solve the problem.

Soo. Now I really don't know what this is about. I checked the systemlog after one of the occasional reboots and there it says "atapi - failure" " \Device\Ide\IdePort0 have not answered within the timelimit" (freely translated from Swedish). I don't know what this means.. and if it's relevant to the problems I'm having.

My system consist of:

Corsair HX 750W PSU

Gigabyte GA-MA790FXT-UD5P, Socket-AM3

AMD Phenom II X4 965 Black Edition

Corsair Dominator DDR3 1600MHz 4GB CL8

HIS Radeon HD 4890 1GB GDDR5

Intel® X25-M SSD 80GB 2,5"

Samsung SpinPoint F3 1TB SATA2


ANY help appreciated.. im goin crazy here.