Can't seem to mirror TV & computer monitor

Got my son a Dell XPS 8700 for Xmas and started setting everything up but I ran into an issue I can't figure out. He had his computer monitor and his HDTV mirrored on his old computer so I figured this would be a snap on his new one. His HDTV is connected via an DVI (PC) to HDMI (TV) cable and that connection works fine. The 8700 came with a NVIDIA GeForce GT 720 1GB DDR3.

When I change the setting on my computer display setting I can't seem to get the HDTV to mirror the computer monitor. If I change multiple display setting to Extend or Duplicate it will briefly display on the TV and then revert back to the computer monitor after saying invalid format.

Now this same setup worked with his 6 year old Dell and a cheap video card so this has got me stumped. If I disconnect the computer monitor it will display on his TV with no issues. What do you make if this?

Could not using a regular HDMI cable instead of DVI to HDMI to connect the HDTV somehow be causing the issue even though it worked fine with his old computer?

I think it's a problem of the resolution of the monitor vs the TV. Most HDMI TVs are 1920 x 1080 (hence 1080p). Based on your screenshot, your monitor is set at 1280 x 1024 which is probably incompatible with the TV. It looks like the card is pushing that resolution to both the TV and the monitor.

I don't know enough about Nvidia cards to know how they work in a dual monitor setup, but it looks as though the monitors have to support the same resolution at the same time.

Yeah, it might be a quirk in the video card. Unfortunately, I don't know enough about Nvidia cards to advise you how to fix it, or set up the dual monitor settings. Sorry.

Can you try switching the cables between the TV and the monitor? That took care of a similar problem I once had.