It is not because of the operating system, if it was the op system it would say operating system not found and just stay there. try these things:
1 reset bios
2 reseat ram in diff slots
3. check if all power cords all plugged in (4 pin, 20/24 pin)
4. chec if you videocard has a power cord going into it, it might have extra power for the videocard
5. well thats all i can think of