What Operating System are you using ?
If it's Windows XP (Home or Pro doesnt matter)
Then there is a feature built into it, that resets the OS if an error occurs.
I have a feeling that when you are recieving the DCC the file maybe (just a guess) corrupt or something else
and windows sees it as an error so resets itself.
To rectify this (Assuming you do have Windows XP installed)
Press your right mouse button on "My Computer" on your desktop and then choose
"Properties" from the popup list.
There should now be a bunch of tabs with stuff like "General" and "System Restore"
Choose the tab labeled "Advanced"
You should now have a bunch of other stuff like "Performance" "User profiles" and "Startup and Recovery"
Choose the "Settings" button from the "Startup and Recovery"
A new box should appear, if you look you should see "System Failure" somewhere in the list of stuff
Uncheck the tick box labeled "Automaticly restart" and then click "OK"
Hope this helps, as i had a similar problem with my XP (reseting all the time while downloading) had a fiddle with
the settings (Amazing what yahoo comes up with if you use Search) (hint)
If you use another OS (ie win 98, ME, or NT) then i'm afraid i cant help you much with that sorry.