I had a computer today with a problem that every once in a while, the internet would stop working. There was no sign of the connection going out (wireless, wired, etc.). You would just be on a website and by the time you clicked the 3rd or 4th link, you’d see a “server cannot be found error”. To further test, I started a hefty download (Windows SP3) and sure enough, 30 seconds in, the download stopped and the error “connection reset by server” was shown.
Windows XP SP2
Hard wired ethernet to router then to cable modem
I tried Winsock fixes, dnsflushing, network connection repair, etc. and nothing helped. I feel stupid just knowing that all it was was that this client had originally been an AT&T DSL customer and had the 2Wire modem/router diagnostics software installed. I removed it and the problem was solved! It looks like this software was running in the background trying to “fix” a connection that was no longer there.