Are you sure that it isn't just Windows 7 turning the network adapter off?
Check the network adapter Configuration, Power Management tab, "Allow the computer to turn off this device to save power" setting.
If your server is always on, then you can untick this setting, and the problem may go away. (I assume it is always on, since you want to run a script that will reactivate the network adapter, and that can only be run on the server if the network isn't working.)
If you allow your server to sleep, then this setting must be ticked, or Wake On LAN will stop working. In which case, you may just be able to send a Magic Packet to the server to wake it, or open a MC Client which will also send a Magic Packet. So if the MC Client is running, you will need to close it and reopen it.
Either way, the first thing I would do is check that the network driver I am using is the latest Windows 7 driver from the manufacturer, not from Microsoft. The Microsoft drivers are often a little behind in fixes, or are actually generic drivers and not specific to the adapter or adapter family.
If none of the above helps, tell us more about your set up. Server always on? Always use MC Clients and not the server to play media? Media Network set up in MC? Using DLNA or MC Media Network?