I have a Linksys router modem that is a number of years old. My computers are connected to it via wireless. After I unplug and plug back in my Linksys, the computers will be connected to the internet for about 30 minutes before they are disconnected. I must unplug and replug the Linksys again before the computers will work again. If I connect them via a cable, they stay connected to the internet and never lose connection. I have completely reset the linksys, but the same problem continues. Any suggestions?