Hello Eryx24, and welcome to Vista Forums.
It could be several things that may cause this. You might run a Startup Repair
if it happens again to see if it may find and fix anything causing it. If you have done any overclocking, then undo it to see if your system will remain stable afterwards. Check to make sure you have the latest motherboard chipset drivers installed. I would recommend that you keep good backups of anything you do not want to lose until you get this resolved in case you are ever unable to restart Vista without a clean reinstall.
Hope this helps for now,