The AV button on my Celestial TV isn't responding to the remote, so I can't change input modes. Everything else seems to be working okay.

SOURCE: How can I turn to AV without a remote control (Samsung TV/VCR 19in Combo)

I had this problem with my TV/VCR combo unit (Samsung CXC1972) after losing the remote while in the dorms. I tried a few different universal remotes and dozens of codes before I tried the Philips 3 device universal remote as pictured below with code 037 programmed into the VCR/DVD button. I can't change the volume with this code but the input key switches between line in and tv. You can also change the channel, access the menu and operate the VCR functions with the code. I bought the remote for less than $10 at Walmart so it might be worth a try, and if it doesn't work you can always bring it back. Hope this helps.

SOURCE: How can I turn to AV without a remote control (Samsung TV/VCR 19in Combo)

you might try going to channel 00
If you cannot just dial the number 00, go to channel 2 and then channel down.
Does not always work, but without the model number of the TV it is hard to advise further

SOURCE: cannot change input source for tv

i would try the abvious first, unplugg the tv from the ac outlet and wait for a few seconds then try turning tv on see if the problem is solved, if not it might be that the key board panel needs replacing.

SOURCE: Direct TV remote "tv input" button won't work with my Sony TV

I came across this looking for a similar solution for my Samsung TV, and I found the solution on ehow.com. Apparently after you program the remote for your TV you have to hold mute and select again until it flashes twice then put in 960 to make the remote control TV input too. Note you're remote should be in TV mode while you do this. It seems silly that the DirectTV guy wouldn't do this when programming the remote.

SOURCE: Can't change TV to AV input.

dont bother trying to do it but then i got the same problem :)