Q: Files deleted from the Library and now internet doesn't work?

Thank you for the welcome, and thank you so much for the reply. Unfortunately, we just tried what you suggested but it didn't work

The message we get when trying to access a webpage is simply "this webpage is not available". No matter what you try to load, it won't work. It doesn't matter if we're using Safari, Firefox or Chrome. Mail doesn't work either, we can read old emails but if you try to refresh and load new emails, it doesn't work.

We tried making a New Location, joining our network like you said, and adding the DNS numbers you suggested, but nothing happened. The computer seem to be connected to internet properly but nothing works. Oh, other computers in my house work fine, it's just my father's, and it stopped working right after he deleted the files from the Library, so we think this is the problem.

My father told me that most of the filed he deleted were .plist, but we really have no idea if this is relevant or not. We can't be sure if every file was restored when the reinstallation was done, but it appears that something is missing and we don't know what to do to solve the problem.

The files were in System>Library. We tried repairing permissions but that didn't solve the problem either.

My father did a reinstallation from the update CD for Mountain Lion (but it didn't do anything), we'll try again with the old operative system that came with the computer. I hope this will solve the problem.

Thank you very much for your help, I'll let you know if it works.

Well, it turns out my father ended up calling a technician... I told him we could solve the problem doing a reinstallation, but he chose to have the whole computer checked (it had other issues, e.g. one of the hard drives stopped working months ago). But yes, the Library problem solved with the reinstallation (that was the first thing the technician did hahaha). Thank you for your help!