Why did my Directv dvr suddenly start recording only one show at a time?

I have Directv and the dvr has always recorded two show at one time as long as you were watching one. For some reason now it will only record one at a time and doesn't record anything else. What is even more annoying is that it won't let you change channels while it is recording only one show. I don't know how to change the setting.

Could be a couple different things that may cause that. Basically you are only using one of the tuners in the dvr. Things that may cause that: Receiver is going bad, if there are BBCs on the back (little black or grey box connected to cable input) one could have gone bad, cut cable or bad cable to one of the tuners.

What model is the dvr?