A fresh install of Microsoft Media Center Edition 2005 may not have the necessary CODEC,as a result when you are trying to view Live TV then the Television won't display correctly and you will get the following error:-Decoder Error - The video decoder has either malfunctioned or is not installed.
1]Download the Microsoft Windows XP Video Decoder Checkup Utility .This utility will help you to determine if an MPEG-2 video decoder or, a DVD decoder is installed on your system and whether or not the decoder is compatible with Windows Media Player 10 and Windows XP Media Center Edition 2005.
2] Next you download and install compatible video decoder which will allow you to view TV without any prroblem.Nvidia,Cyberlink Power DVD,Win DVD or,Sonic will help.Personally I find Nvidia Pure Video is excellent.Remember you just need the decoder not the full or entire package.
Here is a list of compatible decoders:-
*[The last one is Free]