Hello!
I can't see if the problem is software or hardware, but I am hoping and thinking it's a driver issue which make me post it in this section.

I'm new here and I found this forum after days of the endless search of a problem I have. The problem is described further down the post, first background check.

I just bought a new computer. Build it together myself and to help you help here is the system:

Intel Duo E8600 3.0 Ghz
Gigabyte GA-EP45-DS4
Corsair XMS2-6400 TWIN2X4096-6400C5 (4gb)
HIS Radeon HD 4870
Seagate Barracuda ST3750330AS 7200.11 1tb
Corsair HX-series, 520W

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Problem

The core of the problem is that I have a hard time booting my Windows OS. The OS loading gets as far as that loading screen of Windows is done, and right before the Welcome screen or login screen, the problem hits me. Also note that the problem only started after the GPU drivers were installed

I tried to install Vista Ultimate x64, but problems at boot were there as well. This time it usually came up with a Blue screen of Death referring to the process atikmdag.sys.

I also tried to install both Windows XP x32 and XP x64, but this time the BSOD wasn't there. This time a black screen was the problem, and sometimes I got a memory dump in white font color (maybe that is somekind of invisible BSOD).

After a day or so, I noticed that the freeze/BSOD only happened every third or so time I tried to boot the OS.

Note that when not installing the drivers, booting the OS went smoothly. The drivers I got were from the CD, or inofficial hot fixes, or general drivers from AMD's site, all have the same problem. But the problem happened less frequently with the general drivers.

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I have run memtest86 to check the RAM, and the test passed twice without any errors.

I have checked the CPU temperature and both cores idles arround 35-40 degrees celsius (far from abnormal). I have Thermalright extreme as heatsink, and put on Arctic Silver 5 paste. System temperature idles around 45 degrees celsius.

The GPU is in the right PCI-E x16 slot.

Two PCI-E cables from the PSU is connected, and those two cables goes straight to the GPU (they aren't shared with an other device).

I've tried to do a HDD-test with SeaTools Enterprise, but they can't find a disc ("No HBA has been detected").

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Please try to help me. I have a really hard time figuring this out.

Maybe you could try taking the Graphics Card out and using this
Driver Clean Pro - http://downloads.guru3d.com/download.php?det=745
This program will clear out any Drivers related to ATI, when you open the program tick the box "Select Multiple Cleaning Features" and then click the 9 ATI options and start the program it will clean/delete all the Drivers you have installed from ATI (The system only writes over the top of a driver the elements of the old driver will still be there).

Once you have done this put the Graphics Card back in and try installing the drivers off the original CD again or download the latest driver directly of the ATI site, probably best you put the ones of the CD first then update later.

If this doesn't sort the problem then post back, add your Minidumps as attachments in your next post from the Bluescreens if possible.

I've tried with fresh installations of Windows, of all versions. The problem is still there, and that's why I don't think it's a new-old-drivers problem.

I can't provide a minidump from XP, but here is the BSOD I get from Vista x64.

LOL! I can't post a link or image yet, must have five posts with this account. Nor can I PM. Pretty insane restriction if you ask me

When installing the graphics driver are you installing the Catalyst Control Center bundle or just the driver? The CCC requires that you install .NET v1.1 first. Try just installing the driver only which you can get from the ATI/AMD site.

While I haven't ran as many tests as the original poster I am having the same problem and I assume it has nothing to do with my video card(ati radeon mobility 9600) from a hardware standpoint because I am typing this in safemode right now.

At the moment any option other than safemode puts me in a state of endless reboot with a BSOD.

I get the same error message with the atikmdag.sys

I tried uninstalling the driver and reinstalling so far no luck.... I now regret the fact that I don't have system restore running regularly....

well look i just had sorta the same problem but instead i always recieved the BSOD and what i did is removed any extra network adapters not neded and cleared my cache mem. Also i adjust my virtual memory for all drives to the recomended amount. If u can try using a diferent Gfx card to see if ure current gfx is the one causing the problem. I doubt that its ure software since you have already installed various ones. So therfore good luck and dont get a headache.>!

As a disclaimer I don't like scraping things and starting over, which is why I didn't try reinstalling windows.

I eventually got fed up though and just renamed the atikmdag.sys file.

I'm going to have to reinstall catalyst again, but at least I can now actually log on.

I would suggest trying everything on this page first:

www [dot] repairyourpcnow [dot] com /resources/ atikmdag-has-stopped-responding [dot] php

If nothing works from there than just rename the file, but be careful. Disabling the wrong driver is a good way screw your computer up further. (And make you want to punch yourself in the face...