I'm trying to use my Sony TV as a PC monitor via HDMI, but it's not working. I know that all the cables, ports etc. are working but it won't display on the TV. The HDMI output on the graphics card works fine on a computer monitor but not the TV. The TV is almost 10 years old so I'm thinking that the HDMI may not be standard. Everything else displays on the TV via HDMI, including my camera and my Blu Ray player.
 
Any ideas?

John, 
I'm using a Sony TV as my monitor as well.  
Are you sure you're using the correct HDMI (there are usually at least two of these).
I had this problem early on but was able to set it (and leave it)..
 

Check if there is a PC setting / profile that can be assigned to the TV HDMI port.
 
My Samsung TV will output the display fine regardless of the setting, but setting it to PC enable full 1080 x 1920 resolution.

Refresh rate not supported by the (old-ish) TV perhaps?
 
Have you set-up the desktop's graphics options ('output to', 'resolution' etc.) correctly for the computer to use the TV (as an extended desktop I would presume)?

+1 either an unsupported refresh rate or resolution could be the problem. I tried to use an old monitor on a new computer and the new UEFI startup screen was black because the resolution was too high for the old monitor. Once in Windows I could set the resolution to usable values. 

I have tried all the combinations at my disposal. It looks like the HDMI spec on the TV is not compatible with the computer HDMI. Probably not a lot of video cards using HDMI 10 years ago. I tried both of my available HDMI inputs and both fail with the computer. I guess I'm stuck with a 4:3 display using the VGA option. I can force it full screen but the aspect ratio is not quite right.

ampfixer
I have tried all the combinations at my disposal. It looks like the HDMI spec on the TV is not compatible with the computer HDMI. Probably not a lot of video cards using HDMI 10 years ago. I tried both of my available HDMI inputs and both fail with the computer. I guess I'm stuck with a 4:3 display using the VGA option. I can force it full screen but the aspect ratio is not quite right.

I've been using the VGA on my LG flatscreen "TV". I got it to kind of sort of force it full screen using the custom options in the NVIDIA (well... GEForce) control panel. Everything is in proper perspective (as in not stretched) but a few pixels on either side of the image had to be sacrificed... and I had to REALLY screw around with the custom settings.
 
So yeah... if you have a control panel for your vid card try out the custom settings.
 
This however may or may not cause other oddities (I think you saw my other thread(s) about this).
 
Cheers.

What is the TV screen resolution ?

Does this help?
 
16:9 Native 1080p Full HD Resoluton Panel (1920x1080)
1300:1 Dynamic Contrast Ratio (On-Screen CR 1700:1)
1 BRAVIA Engine™ full digital video processor Live Color Creation featuring WCG-CCFL backlight HD Inputs - HDMI™ 1080p (x2), YPbPr (x2) 16:9 Native 1080p HD Resolution Panel (1920 x 1080) 7000:1
Dynamic Contrast Ratio with ACE1 BRAVIA ENGINE
Full Digital Video Processor Live Color Creation featuring WCG-CCFL backlighting system HDMI (High Definition Multimedia Interface) x2 (1080p)

Spec seems fine to me.

The only time I've  experienced lower resolution than what's available on the monitor is in a multi monitor setup where the graphic card runs out of memory - In my case, I can't get my single graphic card to support 3x 1080p monitors. I've since added another graphic card.