Hi,
Try a full power refresh and check if this works.
If it also doesn’t work then there is a motherboard problem.
Here’s the procedure:
Disconnect the charger, remove the main battery, disconnect the RTC coin cell battery and then press and hold the laptop’s Power on button for 30 seconds to drain any residual power from the laptop and also to reset the BIOS back to default settings in case it was corrupted for some reason.
Whilst the coin cell RTC battery is out if you have a DMM (digital multimeter) check the voltage of the coin cell battery. If it is <2.6V DC replace it.
Then reconnect the RTC battery, reassemble the laptop and insert the main battery.
Reconnect the charger to the laptop and turn it on.
Here’s the [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15r-5521_owner%27s%20manual_en-us.pdf|owner manual] for the laptop. Go to p.51 to view the necessary pre-requisite steps and then the procedure to remove/replace the coin cell battery