Our users cannot correctly assist until you provide more data.

* What TV model?
* What video IN ports does the unknown TV model provide?
* From which port on the Optiplex 760 is the TV connected uisng what cable?

The TV is a panasonic Viera and I have connected it with the cable that the old monitor was connected with (blue connection in photo)

@DELL-ChrisM2​ 

It is the desktop model.  

My assumption is that the TV has a Menu that allows you to select VGA as as the Input Source?

If you want to use the 15-pin VGA cable to PC-Input, you might have to adjust your Display Settings in Windows. Sounds like it might be reading the EDID poorly.

I'm assuming Optiplex-760 does not have HDMI or Display-Port ... but if it has DVI (basically HDMI-like digital-signals but missing audio and HDCP) you can use an inexpensive adapter and/or cable.

You can also just put this old TV in your bedroom instead and go back to your old monitor that worked.

@Tesla1856​ 

Thanks, I will have a look tomorrow at display settings. I tried to reply to  @DELL-ChrisM2 but reached a limit on replies? I say this in the hope that he sees it and knows I wasn't ignoring him. The tv input is VGA

OP has Optiplex 760 video output change from small pc monitor to tv and there was Windows video initially on the tv.  It seems the video cable connection is good and tv is set to receive vga from pc.  Spinning dots then blank seems to say pc itself not able to boot into Windows successfully and tv cannot detect an active video signal therefore showing yellow pc mode meaning tv is in standby mode waiting for signal.

We have often hear users move pc or change setup in a very small way then lost pc video output.  First thing to do w this old model (core2 cpu) is replace CMOs battery w a new battery, then clear CMOs settings by motherboard RTCRST jumper. This is first aid to help pc boot successfully.

Clear CMOs steps:

Remove the computer cover.

3. Reset the current CMOS settings:

a. b. c. d. Locate the password (PSWD) and CMOS (RTCRST) jumpers on the system board 

Remove the password jumper plug from its pins.

Place the password jumper plug on the RTCRST pins and wait approximately 5 seconds.

Remove the jumper plug from the RTCRST pins and place it back on the password pins.

4. Replace the computer cover

@jason533​ 

I have done the above suggestions (replace CMOS battery and switch the password  jumper to RTSRST pins etc.) and can open in safe mode, adjust the display resolutions to 1366x768,(the only resolution shown that matches what the tv will accept, but it states that that is WXGA in the operating instructions). When I restart however I am back to square one! Is it time for me to accept defeat or would a DVI to HDMI cable/adapter work better than using the original cable? I can call up F12 boot options if that is any help. It seems I don't know what I'm doing- and that's right, and I appreciate your help everyone.

techluddite (Steve)