Brand new pc, Windows 7 hangs on splash screen!

Have a huge problem, my pc hangs on the windows 7 welcome screen.

It does not freeze, it just shows the glowing windows logo coming together and then they begin to pulsate and it loads for ever and ever, and never stops.

Ive tried alot of things to get it working, and ive no idea why it does it!

I tried re-re-installing windows, and it still does it after a little while!



pre-history.
My new pc ran fine for 3 days, then one day started up with a black screen after loading windows. I reinstalled, but as soon as i installed the ATI Catalyst 10.3 it would go black on the next windows reboot. I called XFX support (my card manufacture) and they told me to use the other dvi port on my pc! and Voila! I had a screen again! But now all of a sudden, it starts with this hanging on the welcome screen thing.

What i have tried so far:

It seems, that if i change the clock on my ram windows starts normally
(does not make a difference if i increase or decrease the clock) and it continues to work untill i shut off my computer for a longer period of time (say 2-3 hours).

Also totally disconnecting the power cables to my power supply helps, then it will start right up into windows.

This is by god the strangest thing ive ever seen!

I really hope you guys can help me!

Regards

Lasse
Denmark.

In the system bios, ensure Plug and Play OS is set to yes, if such a setting exists.

If our suggestions do not help, boot into safe mode + networking. In the start menu search box, type msinfo32 and hit enter. File | save. Then use Winrar or Winzip on the saved file and attach that to a post using the paperclip.