It the ping works, and it should, unless a cable is unplugged etc. then have you got 'map network drive' on startup active. You could also try 'search for computers' and see if what that finds. Right click on 'my network places' to access both . Also was the folder remaned, moved etc?
Can you print on the network? Can Clients see each other and share files, is the problem just accessing the server from a client?
Its something simple,and you should not have to much trouble sorting it. Good luck Kitz e