We have a simple Windows workgroup network in our office. There are nine laptops connected to a router, via 3 network switches. We are using a wired network (NOT wireless). Six laptops are running Windows XP SP3, and two are running Windows Vista SP2. The users access a shared folder on a server which is connected directly to the router. This server is running Windows 7 Pro. Every couple of minutes (sometimes hours), the network seems to dissapear. The users can't access the server anymore, or even some of the other PCs (normally they can't access the XP machines - for some reason the Vista machines appear to be very stable and almost always accessible). Running a repair on the network connection (on the workgroup PC's or the server) doesn't seem to help. Restarting the network switches or router doesn't help either. When I then restart the server however, everthing is fine again for a while again. Any idea what this might be? We have replaced 2 of the 3 switches but it hasnt made a difference. I suppose we can try replacing the router? But I get the feeling it is a software issue - not hardware - as restarting the server solves the problem.
P.S. The server used to have Windows Vista SP2 and had the exact same Problems. We have now formatted the computer and installed Windows 7 Pro but the problem persists. The server has 4 GB RAM, lots of free disk space, all the latest updates and AVG AntiVirus 9 Free Edition.