We're going to need more details to make accurate assumptions as to what's going on.
- How far do you get in the boot process?
- Can you enter the BIOS?
- Can you boot into safe mode/use VESA drivers?
This can be caused by numerous things. Bad drivers and hardware mainly. Whenever I get a problem in Windows a reboot doesn't fix much, you need to fully power down the system to clear the memory modules AFAIK. If you have multiple memory modules you could try booting with only 1 of them (swap between each) to check if ones defective, same goes for multiple hard disks. We'll need more information to be sure though.