Please list Dell model number and version of windows. Ex: Dell Inspiron 3543(3000series), windows 10
If you don't know, type msinfo32 onto the search box, stroll down to System Model, you should see it now.
In the meantime, power off the system, remove all peripherals, AC adapter and then wait about 5 minutes. Replace adapter, power on system, hopefully log-in problem is fix now.