Can't connect to internet when Dell laptop is online

I have an iMac connected to cable modem via AirportExtreme...My finacee has a dell laptop also connected to the airport. When the laptop is online my Imac's internet will work for a few minutes then stop working. It still says Its connected to the airport it just wont connect to the internet. I can join another network and then put my network name and password and it will work for another few minutes then stop working.

When the laptop is off then my iMac will connect and stay connected to the internet no problem.

Do your computer have static IP's? Sounds like a conflict that one doesn't work once the other one is connected...

I believe they do.

May want to switch to DHCP.

Im lost here...when i go under the configuration in my network...

Under the tab TCP/IP:

configure IPv4: Using DHCP


does that mean I'm already switched to DHCP?

still having the same problem,i cant figure this out.