What size PSU are you using? Maybe you don't have enough juice.
What video are you using? If you are using an AGP video card maybe it's the wrong voltage.
OR - maybe it doesn't like that cheap RAM you are using.
You know what to do - try clearing the CMOS, reseat everything and do a selective boot until you track it down. Too bad you don't have some different RAM to try in there.
That's all the ideas I have. Good luck
Which reminds me why I want to start working on a beowulf-on-a-backplane design: I want to be the one to write the program called "clusterfsck."
-- Adam J. Thornton, a.s.r.