1) Well it can be IDM prob cause it have some options like disconnect on complete so Check your schedule setting, Most of the time IDM deals with TCPip.sys so it maybe the case..
2 ) To Make sure is DOwnload clients problem, restart ur machine close all IDM and Flashget startup, try to browse then. I advise you to use IDM or Flashget just one at a time.
3) Uninstall all downloading programme like IDM and Flashget and install IDM at first and see if things are working fine..
4) Try to use OpenDNS replace ur dns with 208.67.222.222 and 208.67.220.220 , See if it works and see you browsing..
I think these solutions would work, let me know if you get any further problem.