Hello hello,
I've been having this problem since I built my new computer with Vista Home Premium (32bit) installed.
Occasionally, when I start the computer up everything seems fine, but my monitor stays blue - this is it's sort of default colour when it isn't receiving input so I don't think it's a 'windows blue-screen' problem.
When this happens I have to restart the machine or turn it off, sometimes resulting in an error where windows then asks if I want to start again as normal or go into safe mode etc.
However, some other times the computer will start up fine with no problems.
What could be causing this problem?