Printer and Scanner

I have a Agfa SnapScan 1236 scanner and a Canon BJC-4650 running Win NT. I have the scanner plugged into the computer works fine. The printer works fine. Plug the printer into the back of the scanner and it locks the computer up each time I restart. I have changed the BIOS settings from ECP to EPP with no effect. I have reinstalled drivers still no go. This was working before, is there a magical way of holding your mouth when configuring this installation??
Thanks for your help I am getting desperate