When using the laptop I cannot type using all of the keys, as some of them are not responding when pressed.

Try what David suggested, but you should also simply try using a different electrical outlet. Or you could try using a new power adapter since there is no light on the power adapter you were already using.

http://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_l...-15-7548-laptop_service%20manual_en-us.pdf This might help lead you in the right direction. It is from the Dell website and is the service manual specific for your laptop.