I've recently installed a copy of Win7 on a build. The oddest thing has occurred ever since the installation. From a cold start the PC boots up perfectly and Windows runs smoothly. But if you try to restart or the system does a reboot, the system never comes back..
It just turns black, no bios screen, nothing. I've tried installing and reinstalling the video card driver, but I can't think of anything else.
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If you boot into safemode, then try to restart from there does it hang as well?
I have seen a corrupt windows update that will not install (upon shut down or restart) and cause the system to hang indefinitely.