Dang, and I had an extra router I got rid of not too long ago. Yup, that's part of the problem. You might still need a new modem, as Keith said, especially if it keeps resetting itself and can't get and stay sync'd. But to run more than one computer off the modem at the same time, you will need a router.
I'm gonna check storage real quick and make sure I don't have an extra router...
jan