laptop modem always disconnecting

I have a toshiba laptop, which is only a few weeks old. My modem continually drops me from my isp. It is not the phone line, because it will stay conneted to my desk top, using the same line. Toshiba tells me its not the modem if it connects. sometimes I can stay on for an hour or so, then it drops me time and time again. And when it connects, it just automatically disconnects. My ISP says its not them. Any suggestions? Oh, I checked my driver for the modem and it is current.