I can't comment on why no DVD... sounds like a switch box or connection issue.
Re. the power source, can you look at the back of the TV to see how it's plugged in? The 120VAC would be plugged in like a normal household connection. On my 12VDC TV, the power feed comes in through small gage wire with a little glass in-line fuse....through a small 12 volt round plug connection into the tV.
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