Are you getting any beeps during bootup?? Also on another forum, they told a guy with the same problem to pull all but one stick of ram...it booted...bad memory module for him....another took his MB out of the case any put it all together on a piece of cardboard and it booted fine, put it back in the case and it booted fine from them on....just some thoughts!! Sometimes these thing can't be explained. other times it can