Disconnection from Internet every 20 mins! How can I fix?

So I have tried going to windows forums, but they are no help! I have been having this problem, which randomly started up about 2 months ago, that I tolerated until it got much worse. My computer randomly disconnects from the wifi, and goes to limited, and from there I have to disconnect and reconnect to the wifi. I have tried everything, even making sure that my computer cannot turn on the wifi. I have a Asus q500a laptop, running windows 8. The last time it happened, I ran troubleshooter, and it said the default. gateway is not available, and it was fixed by resetting the network browser. I have noticed that this happens while i have 3 or 4 tabs open, or youtube open. I need this to be solved, because I use this computer for school work, and I cant get anything done!

Check Control Panel > Device Manager > Locate your wifi card > Right Click > Properties > Power Management
Make sure Turn off this device is unchecked.

Try to connect directly to your router via ethernet if you can, to check if the problems come from your internet connection or your wifi setup.

If your problems are only on wifi then they might come from other wifi networks competing with yours (Maybe one of your neighbors recently installed a new Wifi and it messes up with yours). Try going to yor router's admin page, usually : http://192.168.1.1
Change your wifi channel, try 1, 6 or 11.

You can also download and install inSSIDer for Home ? Discover The Wi-Fi Around You | MetaGeek, it gives you some information on your wifi environment and might help you choose a better channel.