Problem loading windows xp sp3

Hello !!!!!!!!
I have a big problem:
Just after loading Windows XP (Service Pack 3) (boot screen), when I see the list of sessions my screen shows "no signal" and impossible to turn off my computer by a simple support on the button "power", I am compelled to support longer on the button to get to turn it off.
(small precision this bug occurs at the time)

If anyone knows the origin of the problem and knows how to remedy it, I'm taker!

Here's my configuration if you can help:
AMD Athlon 64X2 Dual core processor 4000 +, 2gb RAM, Nvidia GeForce 8800GTS
2 hard drives: Western Digital 500GB
(the computer has no brand)

I think that's all I can tell you!
Good luck and thank you in advance

Hi,
Unfortunately, platforms and AMD SP3 are poor household .
So need to go back under SP2 I think.

Thank you for your answer!
But my computer does not restart loop, and this bug does not permanently, that from time to time.
So even if we do not match perfectly with what is written you think it is still a problem between my AMD and sp3?