Could be a faulty PSU, try a different one?
Also, can you give me your specs??
CPU: CORE i5 3450
MOBO: GIGABYTE H77M-D3H
RAM:4GB SINGLE 1333 KINGSTON
HD: 500GB SEAGATE BARRACUDA
GPU: GTX 560se GAINWARD
OD: SATA DVD SAMSUNG
PSU: themaltake oem
Fan: COOLERMASTER SICKLEFLOW CASE FAN 120MM
Sorry if editing is bad, im new
and its my mates PC, i already built my own and had the same problem.