I formatted and reinstalled a week ago. I don't think it could be a mbr or xp problem. that is why I formatted and reinstalled to rule out software.
Check the following items:
1. Power Supply. As everything is activated, especially if you've got USB devices plugged in. You might need a higher capacity, good quality PSU. With 7 drives, not counting any floppy, you're pushing a 300w unit to its limit just firing up the system.
2. Processor. Is the heatsink tightly mounted with the correct amount of thermal paste? Too much paste is just as bad as too little.
3. Hard disk(s). This was suggested by mah3, and a good thing to check.
4. Cooling issues. Is there proper ventilation between the drives? A clear airflow path near your video card? Do you have enough fans pulling in cool air and exhausting hot air?
5. Video Card. Remember to plug in a Molex or Mini-Molex into your video card if one is required. I know, it sounds stupid. But I've missed the obvious myself. Also, ensure the PCI slot just below the GeForce is empty, to allow cooling.
6. Sound Card. I've had Soundblaster cards not be fully detected, and similar things happen. Physically remove the card and try.
7. Return to the basics. Pull anything unneccessary out, or disconnect the power to any drive(s) not needed to boot with. Kill off two of the three opticals, two or three of the hard drives, extra memory (you can run a Dual-Channel Board with one stick), and any other add-in-cards not needed to boot, then start one-by-one increasing the load.