you can try to test the ram in a friends computer?
as for the PSU...even that PSU has one 16 amp and one 18 amp rail(low for a 500 but still)....so it "should work"
Do you have an old PCI video card to test?
I sugest you take it all apart...then put it together as a basic system.
board, cpu, 1 stick of ram and video....so no HDD's or ODD's... see if it will post then start putting back parts one at a time....
My overall guess is it's ram related....try to borrow some to test it....
Hope this helps