I assume it is the PC's "Wireless Network Adapter" that is losing its connection with the Router?
There are a couple of things to try:
a) Give the PC's "Wireless Network Connection" a fixed IP address, instructions click here
b) Change the Channel number that the router broadcasts on. If you type the router's IP address into your web browser that will open its configuration pages (after entering any Username/Password). In the Wireless settings you can change the Channel number. The default is usually "6" or "11" so try one of these, or the other of these if already using 6 or 11.