Generally, the BIOS comes up before the HD. Can you remove the HD and boot it a bunch of times to see if you can replicate the problem? The BIOS should at least come up and complain about no boot disk or some such. I think.
For strange problems like that, SOP is to open up the case, blow it out with compressed air as best as you can, then reseat everything that can be reseated - connectors, cables, cards, chips, etc. Then wave a dead chicken around the room and boot it up.