Did this just happen with no changes,by you, to your system?
Don't know what your source is for TV cable, sat, over the air etc... but for the DVD player you might want to check the setting to insure it is not outputting to 5.1. I had to set all speakers to "NONE" on my DVDSACD player when I went from 5.1 to 2 channel. Your TV source may be the same. List your DVD player and TV source please.