Hard Drive Not seen by the BIOS

Here are some troubleshooting techniques you can try:
1) Enable boot by USB devices in the BIOS, this makes sure
the BIOS will scan for a USB device when it boots.
2) If Windows see your hard drive, then your hard drive is
working fine
3) if windows does not see your hard drive, you might
have to manually initialize the hard drive through
management console.
a) start>>run>>mmc
b) Click on Disk Management
c) Look for your drive in the console on the right, right
click and choose initialize.

BIOS doesn't need to see the External Drive though if it is an XP formatted Drive it may be invisible to Vista because of Security Issues involved with Vista. If that is the case you need to get your hands on a XP computer to read/Copy your Saved Data.

If you want to try to boot off the USB Drive you need to enable Boot From USB in BIOS if this is supported by your M'Board. But that is very unlikely to work as the necessary drivers for the new M'Board are unlikely to be available.

Col