Network drive not working

HI friends,

In our company we have 4 network drive in our  windows 2003 standard edition server.

We are facing some problems from last 2 months that every day we need to restart our server in the morning if we did not restart it then network drive also did not work .Some time network drive did not work in the noon time but after server restart it start working. i checked event viewer and network connectivity by pinging server, but i did not found any error at the same time when network drive automatically stop working . All client able to ping server but network drive not working. so please help me how to resolve this problem

Thanks