connecting to the internet with my imac

Im new to macs in the past few months, my imac was ok hooked up with the wireless in my previous house but i have just moved and my macbook hooks up to the new wireless network but my imac is picking it up but just wont actually connect to the internet..i hope its something easily fixed...any help folks? something i could try from scratch..ive tried to reset the wireless modem but still no good

System Preference > Network > Airport

You probably have the settings from your old house still active. Clear them all out, let it find the new wireless system and reset itself.