I had this problem on the same PC yesterday with a different drive. Gateway 300X with XP, 512Mb Ram.
Yesterday, I was trying a new USB flash drive I just bought and everytime I put it on this PC, the system would boot up, see the removable drive, bottom Taskbar notice, and reboot. Gave up on it, flash worked on other PC's.
Now I'm installing a new Maxtor 80 G HDD as a Slave and the same PC that failed with the USB flash drive and it does the same thing. System boots, Found new hardware, Identifies it as the Maxtor HD, Desktop screen is up and "BLOOP"! Shuts down immediatly and reboots. Will keep going through same cycle.
We looked at it yesterday as a USB problem because of the removeable but it obviously is not.
Unplug the new drive, run my tests and the PC and system are in perfect shape.
Need this one back up.