Wireless connection...

About a week ago, I got a friend-of-a-friend to hook up a wireless ethernet connection between The computer I am currently using now. Anyway, it worked fine, until one night when my internet just stopped. I wasn't too surprised, because for as long as I can remember, I would regulrarly stop recieving internet connection (Although my computer informs me I AM connected to the tineret and it is running fine), then get it back sometime later (Haven't been able to figure out why, even paid some guy to tell me he didn't have a clue what was going on)... Anyway, lost the connection for a day or two, and, like magic, it came back, unfortunately only on this computer. The other one says it's recieving internet fine, but when I try to use something involving the interent, it informs me it cannot connect. Anyway, I'm totally stumped as how to fix it, and I don't really wanna pay someone to fix it, So I'll turn to you guys..

And yeah, I know jack-all about computers.

Figure out where you're losing shiznit.  Hit run->cmd, type ipconfig /all, hit enter, and make a note of your own IP address and your gateway address.  Then:

ping 127.0.0.1

ping <your ip address>

ping <gateway>

Come back with what happens.