i'd be tempted to do things one tiny step at a time. with old card in, uninstall all drivers, shut down, remove card, and either (a) boot up using onboard graphics to make sure it's clean or (b) boot up with new card and hope it shows up. i'd be more inclined to go with (a) first, maybe even go as far as rebooting a few times, and then move onto (b)
Thought I'd give this a go. I put the old one back in again, and it's doing the same thing now. So, I'm thinking it's a bad slot. I'm not sure how I messed it up pulling out the old one, but I guess I did.
Thank's for all the help.