Find Product Owner Instruction Manuals Some TV's auto sense a signal present and switch the HDMI automatically. You can find out for sure with the manual for your TV from this site
On some tvs the hdmi port are weak maybe its starting to come away from the motherboard , I had this happen with ps4, do you have another port to try ? The only way I could sort mine without hefty repair bill was to use the hdmi port that I was using for Sky and then connect Sky through scart lead.
A DVI cable does not have an audio connection, along with the DVI you still have to run an audio line from the device (DVD player, cable box, satellite receiver) to the TV. HDMI contains both audio and video.
