Tivo?

So overall I've been loving my Tivo, but I'm confused about a few things. Frequently it records shows and the is no sound or picture - just an all black recording. Why does this happen? Have I done something wrong?

Last night for example I was watching Glamour magazine's 50 fashions dos and donts (make fun if you must) before I was going out. The tivo was recording it just fine (I had rewinded to see something a second time so I know it was recording). Then I shut off my tv to go out.

Today I tried to watch the show and it's only recorded up until the time when I shut my tv off. But my tv doesn't need to be on to record these shows right? Why would this happen? It happens frequently too. I have a bunch of stuff that is recorded all black screen with no audio.

The other thing I've had issue with - it's almost impossible to go to my on-demand. If I go to channel 1 - it just shows a black screen on Tivo, but if I go to channel 1 and then use my cable remote to press on-demand it will go into it. But sometimes it randomly kicks me out when I'm watching something. I googled this and didn't find any information about why this would happen. It's really annoying when I'm watching a movie, get kicked out of the movie and thrown into a random show, and then have to renavigate back into the movie for no apparent reason.