One of our computers at my fire station (Using Windows Vista) ocassionlly looses its connection to the internet but remain connected to the network.

I fond the problem one day when I went in to the network connections and choose properties then Internet Protocol Version 4 I noticed the DNS were cleared out (both of them) I have them manually set rather than automatic because when it was on automatic there would be a coflict withour coper / scanner on the network (but it has been like this for a over a year and this new problem just started about a month ago)

I replaced the DNS (used #'s I found on another pc on network) and internet service came back just fine. But unfortunately this has happened 2 more times in the last month.

Anyone have an idea what could be causing the DNS entries to vanish?