Help from a computer technician:
- your computer BIOS has options you can change. one of these is for which graphics card to choose. You can set the ORDER. If it's set correctly then your onboard will be deactivated and your new card will work. See your motherboard manual for details in the BIOS section.
- When you get a new card, such as an HD4770 you will have at least two outputs. If you have a monitor and an HDTV you can output to BOTH at the same time. Usually you would have one as the MAIN monitor (with Taskbar etc) and the second as an EXTENDED. You could drag a Windows Explorer screen or video to the EXTENDED monitor and use it there. If you aren't using the extended screen you should DISABLE the second monitor. This is all done through software for your video card. ATI uses the "Catalyst Control Center."
Make sure to update all your software for your video card. ATI has just the drivers or the Suite (which includes the Control Center). Update the Suite always.
- TV tuner. As said, TV tuners don't tend to have outputs. They use a video player and play it on your screen just like any other video player would. Some setup is needed to detect the channels etc.
Be aware that Canada can not get Digital Channels decoded since 2007 and the USA no longer broadcasts analog channels. Cheap TV tuners will show degraded video quality. I live in Canada. Maybe you can get your TV tuner working for a reasonable price but my recommendation is to get a box from your cable provider. You should be able to get an HD Receiver for less than $200 and add your own USB hard drive or pay more for the full PVR with two tuners which can record two stations at the same time or watch one and record one. We just got one of each; my dad just loves the PVR and it's simple to use.
I've actually heard some success with digital TV tuners and Windows 7 which has excellent TV Guide support (the best you can get actually). A low-power dual-core CPU, and a low-power Graphics card (ex. HD4350), one or two high quality digital tuners etc.
- note that the new DX11 cards (currently only the HD5xxx series) support two hardware video decoders for PIP, such as BluRay video commentary overlayed over a movie
*to be clear, there is no need to physically change your hardware setup. You plug your monitor(s) into the active card(s). If you wish to switch monitors you can make one ACTIVE and one EXTENDED or have one ACTIVE and one DISABLED. You can also CLONE but this is a rarely used feature.
You can probably build a great Home Theater PC including BluRay and TV. Good HD Tuners are expensive, it's difficult to pick the correct parts to make things silent when building a PC. Most people should buy a TV Box such as a PVR from the TV company.