I have a Vizio hdtv and a sapphire HD5570, running windows 7 HTPC. I thought the card had an HDMI but i ordered the wrong version, and got one the has display port, dvi, and vga.
Anyway, here's the problem, I used to be able to get picture on the tv through a dvi to hdmi adapter. I've got hdmi plugged in tv port 2, and sometimes the screen was blank. a simple solution, I would switch to a different input, and then switch back worked fine.
later I updated the drivers and things worked great! it stayed on all the time, no problem and i could even see the boot up process on the tv (before i couldn't until i got to the log in screen). Then because I'm constantly tinkering, i was installing a usb device, told the device manager to scan for new hardware and my screen went blank, and wouldn't come back, even when I used a VGA cable that i had used originally (before getting the dvi/hdim adapter).
I hauled out an older monitor, that worked fine and I re-installed the drivers. dvi/hdmi worked again, as an extended desktop. So I set the dvi/hdmi tv to primary display. turned the computer off, unplugged the other monitor, started the computer up and nothing on the tv. I tried switching off the input and back again, nothing. I plugged the vga cable into the tv and got picture.
later I turned everything down, then turned the tv on, set it to the hdmi input and started the computer. I got picture at the log in screen again. My wife watched tv for a bit (switched the input) and when going back to the computer, no hdmi picture but the vga is working. Tried shutting it all down and starting up again, like last time, no hdimi, yes vga.
so currently, i get intermittent dvi/hdmi and it's not consistent so I can't figure it out. I do have the VGA working, and the weird thing here is that if i check into the screen resolution section of windows 7 or ccc, i see two vga displays listed, the tv and something else (i think a profile for the old monitor I dragged out). The default has my screen extended to this "ghost"display and I can roll my mouse off the side of the screen as if it were extended. I can't disable the ghost display either, nor do I have a second vga device plugged in.
One very important thing is that the TV must be ON and the cable attached into both TV and PC before booting. If not the PC will not "feel" that the TV is still connected and therefore it will not show any picture on it. Have tried to connect my PC to the TV before and know its a bit tricky when you dont really understand how to use the software, I did´nt managed it to work as a separate screen so I kept on using it as an extended desktop.
This is how I did:
The tricky part here is that when you want to see the picture on the TV you must first make the PC monitor as your second monitor and the TV as your first, but when re-booting the PC you first must change the settings back to the normal to get picture on your PC monitor. Have also experied that you got picture on the TV when booting up but it dissapears when Windows is loading up. I dont really know why but it has to be that the settings for first and second monitor port is not done in a correctfull way. Remember that if you pull the TV cable out and re-boot the PC will not show that there has been a secondary monitor connected (the window for second port is grey and un-clickable). If you want to get picture on your TV you must first turn OFF the computer, attach the cable, boot up, go in to the screen settings and change the PC monitor from being the first to be the secondary one (picture will dissapear on this monitor and is shown on the TV instead). Please note that this is NOT the "right"/correct way to do it properly, but just my way to managed something I never understanded!
thanks for the thought, though it doesn't quite solve the problem. In fact doing the boot up that way works sometimes. When it does work, if the tv input is changed, then changed back, the hdmi signal is lost, even when the computer has been on the whole time without going to sleep or anything.
That maybe is so simple that the soon you change TV input the PC will not longer have connection to the extended desktop and therefore requier a system shut down and a new boot to show the "monitor" screen on your TV?