in response to your question about how to change the wifi setting in the BIOS (if there is one); here's the link to the Dell Owner's Manual in PDF that can help you: http://www.dell.com/support/home/us/en/19/product-support/product/inspiron-15r-5520/diagnose?ref=autocomplete#./manuals?&_suid=144699225711103301833258976626
i took the time to download the above document and all the other documents for your model (by the way the full Model is INSPIRON 15R 5520); and unfortunately, the BIOS screens for your model are not shown in the documentation. So, you'll have to just access the BIOS (using F2 key on bootup), and look through all the screens for DEVICES, or ADVANCED OPTIONS, or similar, for any mention of the WIFI or WIRELESS setting. Many BIOSes do not contain a setting for enabling/disabling; so if it's not there, you'll have to pursue other avenues discussed by others above.
I did find a couple of things that may help you howerver. If you check the LED on the front edge of your laptop, as here: http://downloads.dell.com/Manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15r-5520_Setup%20Guide_en-us.pdf
you will notice that in this diagram; the Wifi LED is #14 on the front edge view of the Quick Start Guide page #1 for your model. We need to know what color that LED is? White, Blue, Amber, Yellow, Orange, or Red, or not on at all.
Normally, on most Dell laptops, when the Wifi is on, enabled, connected, and working; that light is White or Blue. Any other color or not on at all indicates a failure of that internal WLAN card as mentioned.
NOTE: The F2 KEY is used to enable and disable your internal Wifi. This is the same key used to access the BIOS on startup. Once in Windows; use the F2 KEY to attempt to enable/disable your Wifi and check the LED as above.
You can also run either the PSA (Pre-boot Assessment) diagnostic or the Enhanced PSA (e-PSA) diagnostic that are built into your laptop using the F12 KEY to access them on bootup. Run through each of the diagnostics if your model has both; or just the Basic PSA if that's all your Model has. It may help to identify a failure in the internal Wifi WLAN card. If you haven't done this, you should try it--it's about 30 min. to 2 hrs. total or so.
All of the other posts here are very helpful, but especially panthera's POST #4. He hits it on the head here. Laptops are susceptible to many kinds of damage, especially drops. Besides the screen and the hard drive, WLAN cards can often become "bonked" by the drop; especially onto a hard surface such as concrete or asphalt. Since your internal WLAN card doesn't seem to be working, and it WAS, you need to make a basic assessment as to whether or not it's working. Not just in Windows. I suggest you download Kubuntu 14.04.1 or later from http://www.ubuntu.com/download/desktop and create a bootable DVD or bootable USB drive per instructions on the Ubuntu website. DON'T INSTALL THE UBUNTU/KUBUNTU ON YOUR LAPTOP!! Just run in LiveCD mode. This runs the program from Memory, and bypasses your hard drive completely. Once Kubuntu loads; you can go into the Wifi icon; lower right system tray wifi icon; click and pick your home wifi network (SSID) and connect. If it connects, then you know your internal WLAN card is working!!!
This will help a lot. This means you probably have encountered a hardware failure so you'll need to test your RAM sticks and your Hard Drive to check there are no problems there. If there are, you'll have to replace faulty components and retest. Once that's done, you can reinstall W10 using Clean Install and retest your Wifi. This should fix it; unless you have a driver related problem; which we can help you to fix. (DON'T DOWNLOAD ANY OF THOSE CRAPPY AUTOMATED DRIVER FIXERS TO DO THIS!!).
If you need help with HW & SW testing; post back, I have a document to help you do this. Allow 2-4 days of your time to go through it however.
Should you still not be able to get your Wifi working, you need to buy an inexpensive USB wifi adapter; they go for about $25-$45 on ebay. Make sure to get a name brand; Cisco/Linksys or Netgear for this test. If you can't do that; borrow a friend's. Just make sure it's working on a modern laptop (doesn't have to be Dell).
If you can now connect to your home wifi network and the Internet; something else is wrong; most likely a Motherboard issue ($175-$400+ to replace). Of course, if the Mobo stopped working with the Internal WLAN card only in Windows (not Ubuntu Linux); it's a quirky problem, and it would be much cheaper (less than $45 US) to simply replace with the USB wifi adapter and keep using the laptop instead of junking it or paying up to $1500 for the Mobo replacement parts & labor it can cost.
Hope this helps. Let us know about the LED colors.
Best of luck to you,
Edited by BIGBEARJEDI, 08 November 2015 - 10:12 AM.