I entered safe mode and uninstalled the driver for the Nvidia card. I tried to install the driver in Device Manager, but kept getting a message that it couldn't find the file.
So I rebooted into regular mode and installed the driver. It seemed to work for 5 minutes, but the issue occurred again.
Another thing that I noticed is that it may not just be the monitor/video signal. I am using ICS to share the network connection from this PC to my XBox 360. In the brief times it works I can get into XBox Live. When the issue occurs I can no longer connect to the network from the XBox.
I also noticed that when I connect this same LCD monitor to my WinXP box it give me refresh rate options up to 75 Hz. When I connect to the Win7 HTPC I only have the options of 59 and 60 Hz.
Any other thoughts?