I have an HVR-1600 tuner card and I am unable to get US station to work on it. I am now using MC7 and was previously using Vista MC. It wasn't working in Vista but I tough it was something related to pnear's hack that I done incorrectly but now in MC7 its easier (again with peter's help) to get ATSC to work in Canada.
On TV I do get a strong signal for US stations but no signal at all on tunar card. I tried with a signal amplifier on the tuner card feed with no success.

Anyone knows what is happenning or has a solution?

First, try some different software (no suggestions here, though -- I don't use Windows), to help figure out if the issue is Windows or the card. Perhaps the native Hauppauge drivers/software would be a good starting point.

Other than that, the HVR-1600's digital tuner is a mid-range unit.
Better than some (eg. HDHomeRun), worse than others (eg. HVR-950Q).

Cheers