I am a student at Cornell University.
We have their wireless internet connection.
I visited porn sites, and now my internet connection is on and off.
I tried XP TCPIP Repair, Malewarebytes Anti-Malware, and System Restore, and they did not work.
Is there a free sure-fire way to fix my WIFI internet connection for good?

Well, probably your best bet is not to visit them sort of sites whilst at college...

But anyways, when you say it's on and off, what do you mean by this?
Does it kick you off once you've connected, or does it not allow you to connect some times?

Do you know if anyone else is having this problem or not? - Preferablely people who have not visited similar sites?

If they had banned you from using their Wifi, it seems a little odd that it would work sometimes.

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The problem in your case is the signal of your Wifi, since it is intermittent. Hence, the solution is to increase the signal of your wifi to have a more stable connection. you can do this by goind to the properties of the wifi driver/device and increase the range of its signal. If this is not possible/has no effect, you might just have to buy a usb wifi ethernet which has a decent signal range. Check this link What gadget should I use to improve the range of my WIFI? | Techyv.com which will give you a guide on what usb wifi ethernet/device you may purchase to improve your signal.