I put the new drive in one of my test machines, and it started booting up XP just fine, so I know there is nothing wrong with the MBR, etc. I slaved the drive and ran chkdsk, which was also just fine. I've been googling around and there are thousands of accounts of this blinking cursor syndrome, but no definite answer (and no situation that seems to be exactly like mine.)
I've reset the BIOS to defaults, removed all extra Drives (CD and Floppy) and I still get the blinking cursor. ANY ideas would be greatly appreciated. I need this fixed for tomorrow, the client wants their computer back.