It seems to happen after the computer takes itself into sleep mode (and not if you sleep it manually).
The symptom is that the network connection icon is no longer "two monitors and a globe", but is now just "two monitors". (It does NOT have a red cross on it.)
Selecting "Diagnose and repair" (after 'diagnosing' progress bar) brings up a Windows Network Diagnostics popup that says:
Cannot communicate with Primary DNS Server (192.168.0.1)
Network diagnostics pinged the remote host but did not receive a response.
Reset the network adapter "Local Area Connection"
Resetting the adapter can sometimes resolve an intermittent problem.
Selecting the "Reset..." control (after 'repairing' progress bar) brings up another popup that says:
The problem has been resolved.Following which the 'globe' reappears on the tooltray icon and normal service is resumed.
This recovery seems to work 95% of the time -- the remaining times requiring a router reboot. (Also, very rarely, the same problem seems to happen without going through 'sleep', but this may be a red herring...so I'll worry about it when the main issue is fixed, if it still happens!)
While this problem exists, normal internet service remains available to two laptops connected via the same router -- one via cable, one via wireless. (The PC is also connected by Ethernet cable.)
The PC is a DELL Dimension E520 running Vista Ultimate. This is a relatively new install (one month?) on a fresh hard drive. We were getting the same problem before the reinstallation, but there were other issues that were clouding the issue. For the first 2-3 weeks after installation it seemed to be OK until I added multiple user accounts -- while running as a single admin user I don't remember the problem happening. Again, this latter 'symptom' may be a red herring also.
Any ideas, please? It is a real problem for the other users of the PC as recovery requires admin access.