|You have not yet narrowed the problem to one particular device. There are two or three possibilities here. Since the laptops can get internet the modem is obviously OK. Are the laptops connected by ethernet cable or wireless? Presume they are wireless. That leaves you with the wired PC unable to connect for some reason.|
You need to experiment to determine whether the problem is in the router, the cable or the PC. Here's how. Power down all the devices. Connect one of the laptops to the router using the PC,s ethernet cable. Power up the modem>Router>wired laptop.
Do you get internet? If YES the problem is in the PC. If NO the problem is in router or cable. Do you have a spare LAN cable to try with? That will help eliminate faulty cable as the problem. You must power cycle the router each time you make a change. I take it you have not used the RESET button on the router?
That may be what's needed but you would then need to re-configure all the WAN,DHCP & WLAN settings. If the ethernet port part of the router has failed you will have difficulty with the re-configuration since router admin management is usually done from a wired PC.
Goin' Fishin' (Some day)