Why does my wifi work but not internet?

[Coolguy11]

I know it sounds weird but wifi works. The problem is that the internet and server doesn't work.

Then, at some time throughout the day, the internet works perfectly for 3-4 even 5 hours.
Then, suddenly, for another 3 hours or so, the internet doesn't work even though the wifi is connected very very well.

I don't know what the problem is. Because i'm in korea, i don't understand what they're saying.
Please help??????? (it's working now, but i fear it's gonna turn off again)