I have a 32" Philips HDTV, with a VGA input that im using as a monitor as I type this. My Graphics card is an Nvidia GeForce 8800 GTS, which has dual DVI outputs. I'm currently using a DVI-VGA connector and the TV is directly connected to the monitor, but is not making full use of the HD compatibility. So taoday I purchased a DVI-HDMI cable from my workplace for quite cheap after the discount
When I hook the cable up properly to the PC and TV and boot, it shows the boot sequence and loads windows, and then the TV gives me a msg saying "video mode not supported" I think it has something to do with the resolution.
You are entirely correct about the issue being the resolution. If you are connecting your PC to your TV and trying to output a resolution that your TV cannot support it will give you that message.
For example, if your TV is only 1080i compatible and you are trying to run it with a computer resolution of 1920x1080 it will give you that error. This is because your computer will output all video in Progressive scan(there may be setting to change this behavior with PC software) and a 1080i TV cannot do 1080p.
Another example is if you are trying to run a resolution of 1600x1200 on a 720p TV. The TV's resolution is actually 1024x720. In that which case the TV would no be able to handle the higher resolution of 1600x1200 or even 1024x768.
you might want to check your TV manual. some TVs have a different set of supported PC resolution depending on the input source eg. connections via VGA connector will have a a different set of supported resolutions and connections via HDMI/DVI will have another set of resolutions. normally, the VGA set is more extensive, while the HDMI/DVI set is more limited albeit fully digital.
you can set your graphic card's output to a resolution supported by your HDMI/DVI connection using Powerstrip or one of Nvidia's utilities. of course you need to do this while connected via VGA, then just switch connections.
Although this can be risky, you can use Powerstrip to set the exact resolution of your TV. For example, I have a Toshiba 37X3030D that has a native resolution of 1366x768. I have my computer connected to it via HDMI from my HD2600XT graphics card. I just downloaded Powerstrip, and set the custom resolution of 1366*768, and the image is displayed on the TV without any black borders or overscan.