problem of internet explorer in win2000 server

[jto]

we are usning internet using firewall and proxy server in my local intranet , and it is working fine at each pc. we are usning a win2000 server for different applications on this server pc after few minutes accessing of any web side is closed , fo getting the internet i have to restart this server again . and after few minutes again problem comes . At this time connectivity from other pc of this server is ok and also firewall and proxy server are pinging from this server but no site is opened and get the massage " page can not be displayed" why any body can solve this problem i will be very greatful to u
thanks in advance