RE: I cannot install wifi and bluetooth drivers for my laptop. (dell inspiron 3521)
On this system model wireless and blue tooth is a combo card. W1703 WiFi/Bluetooth 4.0 combo card and DW1704 WiFi/Bluetooth 4.0 combo card are the two types of cards shipped with this system. If your system is shipped with DW 1703 card, the first driver which successfully installed will take care of the problem.
You need not DW 1704 driver as your system does not have that card. Revert for further queries.