Hello

I recently purchased a new Graphics card (NVIDIA GeFroce 8400GS). It has a HDMI output and have just connected via HDMI cable to my LG HDTV, but the display has has virticle blue lines running down it and video playback is poor.

Has anyone any suggestions why this might be??

In the NVIDIA control panel has the graphics card correctly identified the TV? And has it set the HDMI output correctly? It should set the HDMI to a sensible resolution and frame rate if it has detected the capabilities of the TV correctly.

One thing to check, if it has set 1080p on the HDMI try manually setting it to 1080i. You don't say what TV model you have so it's difficult to be very specific. But I have an LG TV and a HP laptop with HDMI out (though on an AMD/ATI chipset not NVIDIA) and they get along perfectly happily. No lines or any problems playing back video. Though I've only used it for things like iPlayer at the moment.

I presume you are using the latest driver from Nvidia?

I have an Nvidia 7600GT card which gives blue flecks and lines on the screen when playing full-screen videos.
I've always put it down to the latest drivers not fully supporting the card. Also the fact that it's on an AGP interface.

I think all the 8000 series were PCI-E, so this might not be your problem, but in Linux I've always found my card works better on the 173 drivers (if offered) rather than the latest version.

However make sure you have all the other resolution settings etc set properly first, as chrisjr says.