sounds like one of those ie /toolbar/isp/connection issues.
I am using an adsl2 line with actual wires between my computers and the proxy/modem.
if you are using wireless (either in your networking OR internet connection), this might be the cause.
I also have seen toolbars in browsers cause this sort of issue also, and the toolbars tend to set themselves to start up atleast 3 times in the system startup, which means you have atleast 3 copies of the toolbar running at all times, this is WHY I remove ALL toolbars other than the antivirus one.
hope this helps