This took a while to find a fix for that actually worked.
Windows 7 machine. You have a fully operational network card, with correct IP address, default gateway, DNS, etc. So you CAN access the network, you CAN access the internet. However the network icon in the system tray looks like this suggesting it's offline. Hovering over the icon says 'Not connected - no connections are available'. Furthermore the Windows firewall may well show it as being connected to a public network rather than your work or home network. This can actually cause a problem with Outlook that assumes you do not have any sort of connection so it stops retrieving your email or connecting to your online mailbox. Furthermore it's annoying!
It seems the resolution involves adding the local service account to the local administrators group on the computer. Here's the easiest way to do that.
1 Click the Start menu, right click on Computer > Manage
2 Under the System Tools section, double click on Local Users and Groups
3 Click Groups > right Click on Administrators > Add to group > Add > Advanced > Find now > Double Click on Local Service > Click Ok
4 Close all the windows, reboot the computer and then see if it is fixed.