I turn on the tv and cable box and for only a short time I can use the cable remote. After a couple of minutes it won't work so I have to turn off the tv and the cable, start them again and it works for only a little while - what's up with that?
There is a chance that you are getting an IR conflict.
Have a look at this document and try the steps. Let us know how it goes: Troubleshooting IR Conflict - Can't change channel while TV is powered on
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