This is the first sign of a failing Power Supply, or one that has been overloaded by the addition of a power hungry video card or similar.
First eliminate heat issues by checking / cleaning all fans / vents
Then try a known good PSU
For the last couple days I have been having this issue. All of a sudden my computer goes blank, a blue screen appears for a split second and then it restarts. I can't even read the blue screen it goes by so quick. Is there anyway for me to find out what it is saying? Is there a log somewhere or something?