Curious. Have you tried replacing your old card to verify that it still works correctly?
Somehow it seems like it is not getting enough power.
Did you flash the BIOS with the old card still in the computer?
Don't know if this has been mentioned or not, but if you got a 1720 with the 8400M GS like I did and feel stupid for not going with the 8600M GT, you can go through the outlet parts and get the 8600 GT for $144 shipped. And it carries...
I actually have a Swiss brand (Wenger) wengerna.com, and I got the Yukon soft case. But it is incredibly good and fits the extended battery. I also have a 17" aluminum case that is now useless. It fit the 9300 but not the 1720.