Captured video is dark

In the past I have had no problem capturing HDV video from my Canon HV20
video camera via Firewire using Vista Ultimate. The quality has always been
excellent. I just tried capturing some video and the video is coming in much
darker than the video that is displayed on the camera. I can play previously
captured video and is looks fine on my monitor so it is not a video setting
problem. I have tried capturing the video with Windows Movie Maker, Premiere
Elements 4, Pinnacle Studio 12 and Nero 9. All them look the same. I
recently installed updates for my video card driver (dual NVidia 8800 GTS's
in SLI mode) and for DirectX. This appears to be a hardware/driver issue.
Any suggestions for troubleshooting this issue? What controls how the video
is captured over Firewire? Is there possibly a codec that has changed that
would affect video capture? Each of these programs saves the captured video
in a different format so I wouldn't expect in to be a specific codec, unless
something is used by all of these programs. Could there be something wrong
with the Firewire cable or port?