Computer Disconnects - Can't Found Network Setting

my computer seems to keep diconecting from the net, wellwhen i say it disconnects, i mean that when i first put the comp on its fine then after a few mins i cant get any pages up the little tv screens dissappear from the task bar and any browser iuse says page cannot be found if i go into my network settings it says i am connected and if i rebooteverything is fine again, imrunning windows xp and using telewest cable modem even tryed ispconnection test and it says it is fine, stepson is running wireless of the same cable modem and has no problems.