I had exactly the same issue with my N7260 wifi card (lenovo z510) and I know how frustrating this could be. My solution below:
I'm using Windows 7, but there was a DVD with drivers attached to my z510 for Windows 8 (at least that's what is says on the DVD). I've browsed thru the WLAN drivers on that DVD and finally found the ones that worked for me
PLEASE NOTE: Before I installed these I've deleted N7260 from my Device Manager and I also removed all software in Add/Remove Programs that had anything to do with my WLAN and it worked
Here's the .zip package with Intel drivers. BTW. I have no idea why it's so large. When you unzip it it will be over 600MB. Anyway, choose the right version (x32 or x64) and install it:
Good luck!
