Roll back your computer to the last known good restore point.
If that fails, do a hard reset on your camcorder. There will be directions on the internet showing how to do this.
Might be the obvious, but have you rebooted? I've found that with my HDSC card, I have to reboot before using it. Even if I use it, then remove it by ejection now, in order for it to work again I have to reboot.