Radeon hd 4870 to TV

I have a radeon hd 4870 and have connected it to my tv via a vga connection cable(with the apporpiate adapter on the video card side) and when windows was booting up it worked...but now it says unsupported video signal..any idea??

If you can see it while Windows is loading, the AMD video drivers haven't loaded at that point. It could be a bad cable. It could be bad drivers. It could be a bad port on the TV or the video card. It could be an adapter issue (Is it DVI or HDMI to VGA?).

Any or as many answers you can provide to the following questions will help troubleshoot this issue.

Does it give you the "unsupported signal" message at about the time it should be asking for your login or when the desktop would be displayed (if you don't have multiple logins on that PC)?

Did you just start using the TV as your monitor? Or has it worked in the past? When did you last update your video drivers? Did you get them from AMD, your video card manufacturer, or Windows update? Do you have a PC monitor you can hook it to with a VGA connection to see if it's a consistent issue across displays? Does the TV work with other devices running through this VGA connection?

Yeah. The DVI connector is usually white. You may have the refresh rate set to something the TV set supports (60Hz or 120Hz are common) set too high, too low, or at some level the monitor just doesn't accept.

Ran into this multiple times. As ubercake mentioned It may actually be setting the resolution wrong or too high.

Boot to VGA safe mode, if you get into windows that's exactly what the issue is.

Not a major problem just mismatched settings. Set the res to something small like 1024X768 ... reboot normally and then adjust resolutions from CCC

Happens all the time on ATI cards