Black Screen Hangup

My computer is a custom computer I built it myself. It has a dual core Intel

1.5 GHz Processor, 2 GB of memory and a 350 gig hard drive.

It is running Windows Vista 64

My problem is some times when I go to boot it up it goes thru the post test

and starts to boot. BUT then the screen goes black ( with a dark glow ) it

will stay that way for five to 10 minutes, and no matter what I do it will

not boot up until it is ready up to 15 minutes.

Then it will operate normally until another MS update comes along,

Any suggestions Please.