media center won't burn dvds

I've been burning tv programs from media center to dvd. This has recently
stopped working. Using: Vista, Media center, Nero 8 installed since
Realplayer installed and uninstalled, Have tried system restore but my
furthest back options are now gone (used). What happens: Click on Nero or
sonic, Nero will not accept show when it is clicked on(size available does
not change, when go to burn says problem occured). Sonic tries (used to work)
Media center says extensibility host must close and burn is halted. HELP ,
my drive is rapidly filling. (I work evenings)

Winn