Wireless shows as connected, but no internet!

I tried searching for this but couldn't find any threads with my specific problem. If a thread already exists, I apologize.
I have wireless and it everything was fine, until I took my MacBook out and then back home. When I tried to connect to the wireless as usual, everything looked normal (airport is on, all the bars are lit up, correct network, "Status: Connected") but there is no internet. I tried Firefox, Safari, MSN, nothing is connecting. I've tried restarting, unplugging the modem and router and waiting a few minutes and then plugging them back in, the wireless still shows it's connected, but no internet. I tried plugging in an ethernet cable and my MacBook recognizes that it's plugged in, but still, no internet. I know it's the MacBook and not the internet connection, because there are two other computers attached the the same modem that work fine. I have changed nothing on it, no settings, nothing, this happened all of a sudden.
I am quite computer illiterate, so if anyone is willing to explain this to me as simply as possible, I would greatly appreciate it.

Note: Moved to appropriate forum.

You said you took your MacBook out and then back home. I assume by that you mean you took it out and connected to another network?

If that's what you did, your MacBook may be "lost". How about trying this and see if it helps: System Preferences -> Network. What are you showing for "location" in the location box at the top of the dialog?

If you're not showing the correct location (for example: home) then your MacBook may not connect to the net either wireless or ethernet. Your location may have changed when you took the MacBook out and connected to another network.

Regards.

Yes, I took it to school and used their wireless.
Under location it lists the date and time when I last connected. It's always been like this, I've never seen it say anything else... No idea what that means or how to change it to see if it will make a difference.

I find it sometimes helps to turn the airport off (via menu bar) wait a few seconds and turn back on. It then reconnects to the AP and often works.

Ringo665 said:

Yes, I took it to school and used their wireless.
Under location it lists the date and time when I last connected. It's always been like this, I've never seen it say anything else... No idea what that means or how to change it to see if it will make a difference.

Click to expand...

Let's try to change that to what it should be: Go to the location box that I pointed out to you in my last reply, click the down arrow and set it for "Automatic". Let's see if that makes a difference. If not we can try something else.

Regards.