Dell Venue 5055 no power LED but vibrating when trying to charge

Hello,

I have a Dell venue 5055 Pro tablet that was working the other day after a long period of inactivity. The battery was at 16%. I shut it down after a short usage, and tried to charge it with the Dell power adapter and (what I think is) the original micro-USB power cable that came with it. When I plug the powered adapter into the tablet, the LED does not light up. There is a small vibration about half a second after I plug in the adapter. Then it vibrates again about 3 seconds later.

The outlet, adapter, and cables all work for other devices. I've tried holding down the power button for 10-20 seconds in various scenarios (while plugging in, after plugging in....). Nothing happens.

Any ideas what I should try?