I tried everything suggested in these posts with no luck and after months of randomly limited WiFi and general connectivity problems on Windows 8.1 I finally managed to get it to work properly. I figured this out, pretty much accidentally, but it works.
In advanced TCP/IP settings under IPv4 protocol settings put Gateway and Interface metric to 1 instead of Automatic. Now PC connects to network a little bit slower than usual, but with no connectivity problems.
This is mostly for people with Intel WiFi card, Centrino-N 2230 on Lenovo ThinkPad 530c in my case, because picking Intel driver from list instead of Microsoft's (like suggested for Broadcom in some comments) won't work. Hope this could help.
.....And now I'm back online. I've reposted his comment because, like me - he tried to fix this problem for months! Hopefully, this will help the next person.
I am truly grateful for all your help here Jonathan! -Jeannie