I worry that this card has issues. Yes you can try another HDMI cable and drivers but frankly I'd challenge the seller that called it new. This may be why they sold it off.
Last night I installed a new graphics card into my computer (Nvidia GeForce 550ti). To do so i had to rewire my entire computer power supply with a new supply because my original was not strong enough. New power supply is an EVGA 500B. I am using a TV as monitor with an HDMI input. To get the correct display settings so i could see the display on the TV i hooked up a regular monitor through VGA.
It ran perfectly for well over 3 hours. As soon as I unhooked the extra monitor, the TV went black. After testing the connections and uninstalling and reinstalling the device driver for the graphics card it does work without the monitor but only for a limited time. (roughly 30-60 minutes) At which time the TV loses display and the only way to get it back is a hard reset of the computer. It runs for 2+ hours no problem with the second monitor plugged in but goes right back to losing display after a short time if it is not plugged in. (keeping the second monitor is not an option at this point)

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