First, go into the router from one of the pcs that works now.
Go to MAC address filtering on the left-hand page menu. Add the MAC address of the new laptop (Clue: type ipconfig /all at a command prompt).
Then click LAN Settings on the menu page. heck that there are enough addresses available between the IP Pool Starting Address and the IP Pool Ending Address. Click Apply Changes.
Exit the router.
If you have switched off SSID broadcast, you will have to enter the SSID in the laptop wireless set-up; similarly if you applied WEP encryption you will have to enter the codes.