My COMPUTER spontaneously reboots at various times when I try to backup by master and slave drives.

Quick background.  My 8yr old 60G hard drive finally died so we upgraded.  We updated to a 120G as the master and bought a 300G Seagate external for a backup drive.  My system has a DVD and DVD-RW drive, a 120G and 160G hard drive (master/slave, respectively), a 3.5 drive, and three fans running off of an Antec TruePower-2.0 430W PSU.  My speakers, 22" Flatscreen, modem, router, and printer as well as the external drive each have their own AC power supplies.

I READ on a couple of forums (COULD not find one here) that said a spontaneous reboot during something like this is almost always a PSU issue.  One problem, my external drive has its own power source and it only reboots when I attempt to back up my master/slave.

Any ideas?  Thanks in advance.

ZDoes the 300G external have it's own power source ? ?

If not you might want to invest in a USB enclosure that has one. That's a large draw for a USB device...