I guess you meant, you have wireless connection to your router. The router is connected by wire to a modem, that connects you to the internet, right?
Anyway, how are the PCs connected to the router, wired or wireless?
If they are connected wirelessly, try to connect one of them by wire and check out, whether the problem persists.
The original poster should always write the last response !!!
Let us know, if the problem is solved !!!