Hi @matinr1
Here is a list of the [https://www.parts-people.com/blog/2014/06/25/dell-inspiron-15-3521-beep-codes-diagnostic-indicators/|"beep error codes"] for your laptop.
When you turn on the laptop, count the number of beeps. They will occur in a repeating fashion with a pause between each set, e.g a 4 beep error code will sound like, 4 beeps -pause-4 beeps pause etc.
The code chart will give the reason for the failure and below that there are some repair options for each error code.
Hopefully this is of some help