I have a modem with wifi at home but my phone cant seems to surf internet tho its connected to the wifi, why?

My brother is using an android phone and I'm using an iphone now, both our phones can go online when we connect to the public wifi like mcD's wifi etc, but when we tried connect it with our own house wifi, it cant seems to surf the internet. altho it shows connected to xxx on the phone, but we still failed connecting the internet. The phone's repairman says its the modem that's having some problems, according to him, we must change some settings of the modem. Does anyone knows what setting is that? or is there any other solution for this?