Replying to Macbook Pro Help Needed!

I was using my macbook this morning, skyping my friend, facebook, etc. I came back to it 30 minutes later and I tried to open up Safari, but it said I wasn't connected to the internet. At first, I had full bars, but then it switched to an exclamation point over my bars saying I'm not connected to the internet, even though I have my wifi selected and I had used it just a little bit earlier. I tried restarting my computer,turning airport on and off, etc. but nothing seems to be working! Please help, I need to use this thing soon!