What could be wrong?

[stlnewport]

I Have a Lanpaarty nf4 sli-dr, it works fine ,but after i shut down the system in about 20 secs the ram l.e.d. starts blinking along with the standby light and i can not power the system back on unless i turn off and then back on the power switch on the psu, which is an ocz power stream 520. I've taken the whole system apart and put it back together, but still nothing. Any ideas would be helpfull thanks.

[stlnewport]

aero cool case

dfi nf4 sli-dr

amd64 3000 @ 267x9

ocz 2x512 2-2-2-6 @3.2v

power stream 520

300gig maxtor dimondmax 10

plextor 716-a

leadtech 6600gt @ 685 and 1178