Hi @radicki ,
No idea why this is happening unless you pound the keyboard as this will cause the key contacts to wear or perhaps the circuit membranes to fail.
Try connecting and using a USB keyboard just to eliminate the possibility of a software problem.
Here’s a link to the [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15-3537_owner%27s%20manual_en-us.pdf|service manual] for your laptop, taken from this [https://www.dell.com/support/home/us/en/04/product-support/product/inspiron-15-3537/manuals|webpage].
Scroll down to p.21 to view the necessary pre-requisite steps and then the procedure to remove the keyboard. The replacement procedure follows afterwards
Replacement keyboards are available online. Just search for ''Dell Inspiron 3537 keyboard'' to get results for suppliers of the part.
Hopefully this is of some help.