Reboot in cold boot only

[joyful_winner]

My computer will restart everytime when cold boot(i will unplug the power of the tower after i shutdown my computer)....but it only reboot once in cold boot.Then everything will be fine. Windows will show error message....
When i sent the report to microsoft, it will state something wrong with the video...
I tried to reinstall the latest video card driver. Replace a new video card....
Same things happen
Do memory and hdd diagnostic test all works fine.
Try to reinstall the windows....Same errors happened....
Guys....Do you have any clue on what's wrong....?

Thanks very much for your help!!!

Here are the Spec....

cpu: intel 805 2.6GHz Dual core
mb: asus p5vd2-mx
ram: smart 1g ram
hdd: samsung sp2504n
video card: sapphire x550 512mb(original) gigabyte x550 256(replacement)
OS: windows xp home sp2