You may have already done this but try....
Get into the bios then read the MB manual page for page and set up the bios accordingly.
Now you may have some memory that's going down or intermittently going down. If you have two lots, reduce this to one and try booting again, then try the other strip of memory.
Whilst messing around with memory, check every plug in on the board and carefully check the cables and wires going into the plugs. If you have any spare ribbon cables for the various drives, then change them.
Best of luck.