Many Inspiron 15 5000 units use a Broadcom or Intel Wi-Fi card. Windows 7 lacks generic drivers for newer cards, so you must download these beforehand.
Once you have installed all the , follow these best practices: Dell Inspiron 15 5000 Series Drivers For Windows 7 64-bit
Why is this important? Installing a chipset driver for a 5559 on a 5548 could lead to blue screens or system instability. Many Inspiron 15 5000 units use a Broadcom