Nad 6100 Cassette Deck plays a few seconds just fine then stops

Thanks in advance for any help. I just bought this and the head looks good and the rubber wheel thing spins and is nice. But, I tried 3 tales and each plays a few seconds and then the deck stops itself. When I pull the tape out, it has a tiny loop about 3/4 inch high that did not go into the rest of the shell like it should. I guess there is something that needs to make the tape wind up that is the issue. The sound is clean for the fee seconds and the unit is in great condition. Even came with the box. It is the 1988 version. I think there is only one belt in it and I am not scared to try to fix this. Please help if you can and advise me as to what I can do. I really like this new toy and am excited to get it working right. I won’t test anymore until I get some answers, but its behavior is consistent. Thanks in advance!
Check the clutch on the uptake spool. 
When was the last time the heads, pinch rollers and capstans were cleaned?  If there’s a belt on the take-up, it’s probably dried up.
Thanks, noromance and rodman99999. I just got the deck today and do not know its history. I will look into this. I am cleaning it now. 
Your best bet to get this thing working right is to repair it. 
It’s probably a dead spot(s) on the cam motor (corrosion/from sitting idle for long periods), or the back tension belt needs to be replaced. Both can be an easy fix.

To free up the dead spot on the motor, take a sacrificial cassette and remove all the tape inside, just pull it out and discard, just leaving the reels inside to make a “dummy cassette”. Put the tape inside the deck and press play, let it run overnight or 24hrs. Next day try a regular tape and see if it plays.

If it still doesn't work replace the back tension belt. To access it, remove the cassette door (slide upwards), and the back plate (2 screws) in the cassette well and you will see it there to the left. MARRS sells an exact replacement.

If if it still doesn’t play, then the cam motor needs to be replaced. You may need to find a donor deck, I believe the Nakamachi BX-300 uses the same transport. But it it wold be more cost effective to find another NAD deck.
Thanks for all of this info. I can report back now that I belt a belt from Germany and with the help of a kind soul who guided the process, I changed the belt and pinch roller. I also used a 9 volt battery to get around the dead spot and the deck will ff and rew, but will just click about 5 times and stop totally when I push play. I then have to turn it off and then on again for anything to work and still same. Does this suggest it is the cam motor or the reel motor? I am not sure about the clutch, but will keep looking - not sure of proper names and which is the uptake side, but will investigate. Thanks for the help! I so want to get this working!