Also if the USB adapter has an extension lead, you might want to try connecting that and moving the adapter further away from the computer and closer in the direction of the router to try and avoid any interference the PC might cause.
You might also try moving the router physically closer to the PC, if that can be done (it might not if your modem is also there and there isn't much room for the telephone or cable line). Some routers have the option of turning the power (in decibels, dB) up too, which will increase range on the device so it might not lose the connection as much.