ok..i took the PSU to an older PC (Athlon X2, 3600, M2A-VM onboard graphic), and it boots up fine...
Soooooo.......does that mean the mobo or something else is fked? or it could still be the PSU? (btw, the older PC which boots up fine uses the extra 4-pin connectors instead of the 6-pin connectors)
Unfortunately I don't have another PSU to test the new computer atm.