HK AVR254 - video display cuts out as soon as source is selected
I recently bought a second hand Harman Kardon AVR-254 7-channel which the gentleman said was working fine for him, but had been sitting unused in his office for a few months now. When I got it home and installed, it powers up just fine, all the lights on the display panel work, however the video display to the TV (through HDMI cable) only works for a short time to show you the setup menu and then as soon as you select a video source, it cuts out. The receiver stays powered up and display panel still shows everything, just no video output. If you turn it off and back on again, you do not get any display (cannot get to the set up menu). I let it sit unplugged overnight and tried again in the morning and was able to get to the display menu but then cut out again when I selected a video source. I haven't been able to get audio out of the receiver either, however I have only tried the radio source AFTER the video display cuts out. I did follow the manual in setting up the speakers, inputs, outputs, etc. and ever followed the factory reset process twice without any luck. The display did not kick back on after the factory reset. The display only works after letting it sit unplugged overnight.
With my very limited knowledge, the only thing I could think is that something is shorting the system when I select a video source? The TV is an older basic HDTV (a 42" Sanyo Flat-screen bought about 4 years ago) which I honestly don't know if it is 720p or 1080p. I'll take a look tonight when I get home as I'm sure it mentions the resolution on it somewhere on the TV. I can't imagine it would, but could it cause issue if the receiver is trying to push a signal of 1080p resolution to the TV if it is only 720p? Would the "version" of HDMI cable make a difference? I'm not sure which ones I am using. One is brand new from our cable provider, the other was in my drawer of electronics, so is probably about 2 years old. I did confirm both cables are fully functional as they will take AV signals directly from the cable box into the TV.
I'm a beginner to the AV world, so I just bought a fairly basic home stereo set up so I wouldn't have to spend a lot of money (currently set up as a 3.1). There is a good av repair shop here in Charlotte, however I'm worried it will be $100+ to diagnose and fix. I wouldn't want to spend that as I could get another basic used receiver (would want a demo this time to confirm working condition) for less than that.
Just looking for any advice you can provide.