[C E Jones]

I'm running an HTPC using a plasma tv as monitor, connected via HDMI. It's been working perfectly since I built it 4 months ago, but all of a sudden I stopped getting an image on the tv, just a blank screen with a "no signal" message flashing. I thought it was a problem with the HDMI connection, but when I hooked up an lcd monitor via VGA, same thing, just a black screen. I know the monitor works because I tried it on my laptop.

What could be causing this? It could be that the graphics card went caput, but I doubt this as I bought it brand new 4 months ago, and have never had a problem with it before. (It's a Sapphire Radeon 4670). Could it be a virus? I've even tried booting from a Windows CD, and get the same thing. This is very frustrating because I have no way of troubleshooting without beeing able to get a picture. Is there anything I can do? Anything at all??

Edit: I know the rest of the computer is working fine, as when I load a music CD it plays it automatically--so the computer itself is running fine.

[Carbon]

It sounds like the graphics card to me, possible other causes the PSU half-dead (enough to power the rest of it but not the card), or just a loose power cable (although it would usually scream at you instead of just not working).

You're just going to have to troubleshoot part by part - frankly I don't see the point of building a HTPC without integrated video anymore now that it can often push 1080p content often over HDMI but if you built this a few years ago I guess it makes sense.