Disconnect all peripherals and confirm if system is working fine with AC Adapter only. Kindly confirm how old is the Battery?
Remove AC adapter, Battery and drain flea power. Remove the battery and charger/ac adapter/power cord from your Dell notebook, press and hold the power button for 20 seconds to discharge any residual current inside the laptop. If still not resolved, follow next step.
Check the AC Adapter status in the BIOS. If AC Adapter status shows Unknown / Not Detected, then try changing the Ac Adapter.
Let me know the Results.
Thanks & Regards