Battery is probably dying. Try removing it and using the adapter alone. If that works--  Use the laptop as a desktop replacement. Make sure the adapter is not loose in the connection and is recognized in the bios. 

See this about today's battery life of only 18-24 months or less--

https://www.dell.com/support/article/en-us/sln128667/dell-laptop-battery-frequently-asked-questions?lang=en

You will have a hard time finding a genuine Dell replacement battery from Dell or Dell Parts. Stock has run out of many models of batteries. I did find this if you want to spend the money but make sure to check out compatibility with your exact model--

https://www.parts-people.com/index.php?action=item&id=29927&utm_source=google&utm_medium=cpc&adpos=&scid=scplp29927&sc_intid=29927&gclid=Cj0KCQjwn7j2BRDrARIsAHJkxmwo0PJvkfOAm1lTIAw1GMEY93UOE5I4uSQbYfcDNnw49RfrIAl_rRsaAuxJEALw_wcB

Batteries do weaken even sitting on a shelf. I would use the adapter alone and save the money. Don't buy from private sellers on the net or in marketplaces like Amazon or Ebay. Lots of scams with replacement batteries.

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