Wireless internet problems?

My dad recently got a new laptop its a satellite c665 with windows 7. When my dad tried to connect it to our wireless network it totally screwed up the network. my dad was able to fix the internet for the main computer but the laptop and the other computer dosent get wireless internet even though when we connect it it says the signal is strong. The router is a cisco linksys rangeplus wireless router and the modem is a speedstream 5100 ethernet adsl modem. Our internet provider at&t said the problem is with the router. What do you think?