I SOLVED IT!!
I have HP Pavillion TouchSmart 14 PC which has Intel wireless driver and my modem/router is Cisco.
My connection was also dropping to limited connection and I tried everything else on the web (updating drivers, resetting modem, power settings,... etc) but none of them has worked until I disable my bluetooth driver!
Most probably there is an interference between wireless driver and bluetooth driver which is cannot be solved even the last version of driver software.
Before I disable my bluetooth driver, I encounter "limited connection problem" every 10 minutes and the only solution was resetting the computer which was annoying me. I prefer to use my cell phone to surf in the internet, but after I disable my bluetooth driver I have not encountered any limited connection problem for 2 WEEKS!!
If you want to disable your bluetooth on windows 8.1, click start and type "bluetooth" and click bluetooth settings on the search pane. In bluetooth settings window, turn the setting to off.
I hope it would work for all of you!