Macbook cannot connect to internet but is connected to router

Hopefully someone can help me solve this - I have a late 2009 MacBook Pro, running Lion, never had an issue with internet until now, but everytime I wake my computer from sleep, I see the dreaded exclamation point over my wireless signal. My computer knows it's connected to our wireless network, but cannot connect to the internet.

All my other devices (iPod Touch, AppleTV) are working fine with the internet, and my computer is connecting to other wireless networks fine as well. I've tried resetting the router, completely doing a hard reset and creating a new network, all to no avail. I've tried revewing the DHCP license as well, to refresh the IP address? didn't seem to work.

I'm afraid I created this issue with the network in trying to fix my homesharing problem - I can't get homesharing to work between my computer and AppleTV, even though all the settings are correct and I've gone through the troubleshooting page on both several times. I began fiddling with router settings, then it worked very briefly, then this connection issue with my computer started.

Any ideas or suggestions on where to go from here? Anything would be appreciated.