ATI 8500 TV Out problem

I have had my ATI Radeon 8500 DDR VIVO since around the time it first
came out. For the most part it seemed to work OK. Recently placed
the card into a new motherboard, an ASUS P4P800-Deluxe. All seemed to
work fine in my test area and when I plugged it into it's final
location with all the connectors plugged in, the system started the
BIOS screens, then went blank before it started looking for a floppy
disk, or a CD-Rom drive, or the hard drive. The Viewsonic monitor
keeps clicking. Went back to the test area and all was fine again.
Traced it back to the S-Video connector on the TV out. When it's
plugged in on initial boot-up, this problem happens. Remove the
connector and it starts fine. I believe you can plug it back in after
that fact and the TV out works, but haven't bothered to try till I
find out what's really going on here. Any suggestions? Thanks.

JR