Computer wont boot HDD with windows 7.?

I am working with two computers. My friend's is an emachine d4362 (basic specs: P4 3.0 ghz processor, 3.2 gigs of ram) and mine is a Soyo Dragon. (basic specs: P4 3.0 ghz processor, 1 gig of ram) The emachine had windows xp installed on its hard drive (IDE hard drive) and it ran perfectly fine. We wanted... show more I am working with two computers.
My friend's is an emachine d4362 (basic specs: P4 3.0 ghz processor, 3.2 gigs of ram)
and mine is a Soyo Dragon. (basic specs: P4 3.0 ghz processor, 1 gig of ram)

The emachine had windows xp installed on its hard drive (IDE hard drive) and it ran perfectly fine. We wanted to install windows 7 on it, so we put in the disk. it always froze at 16%. So we put the hard drive into my computer, and loaded ran the installer. It again froze at 16%. Another method i had learned of was to install from a USB drive. I did that, but his computer wouldnt boot from USB. Mine, however, did. So we put the emachine's hard drive into my computer, and booted from USB. We successfully installed Windows 7.

Here is the interesting part. On my computer (the dragon) windows will boot normally, and go to the windows 7 desktop without a problem.

When we moved the hard drive back into his computer (the emachine) before it even gets to the "starting windows" logo, the computer automatically restarts. So the moment the hard drive is being accessed it just shuts off and tries booting again. I dont understand. why will it work on my computer and not his? (remember, this hard drive was ORIGINALLY in his computer to begin with, we only switched it over because his computer wouldnt boot from USB)
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