okay, lots of possible reasons for this error. ;)
1. Check that cpu and ram is seated properly, and see if you didn't accidentally have bend a pin in the cpu socket (can be very hard to see, but try to look anyway)
All the ram out and re-seat them.
Also check that all other connections to the motherboard (incl. PCI) is properly seated.
2. if that doesn't help, then try the PSU in another pc (if possible), or maybe try to use another PSU. -To isolate that as a factor.
Maybe try to boot with only one RAM stick, and try the sticks in different ram slots.
3. Try to boot using another graphics card. Maybe if you have an old one, or you can borrow one somewhere.
4. Still no luck? RMA the motherboard and the PSU together (if you bought it the same place). :)