Inspiron N4010 won't connect to wireless network, but it used to

The network connectivity indicator in the lower right of the screen has a "!", and says "No internet access." But when I left-click on it, my wireless network is listed and it says "Connected." My MacBook is connected to the same network without any issue, and the N4010 was connected a few days ago without any problems. No settings have been changed. I have unplugged the modem and plugged it back in, have restarted the computer, any other ideas?

The laptop is a two-year-old Inspiron N4010 and the modem is a SBG6580.

Help?!