Have you tried running System Restore? If that works, you could try installing your updates one-by-one and checking on your internet access after each one. That might give you a clue what was changed.
Hello: My Dell XPS 8300 has been connecting to the internet without a problem for months until this morning. This morning the computer will not connect either through the LAN or wifi adapter. The network tray icon has the yellow triangle and says "no internet access." I have reset both the computer and router multiple times and I have also unplugged them in between. Other computers in the house connect to the router without a problem wirelessly. This leads me to believe there is something wrong with the networking/system software configuration. The computer can't ping the router. It may be the software/system config was corrupted in the last 24 hours and I may need to reinstall the operating system which I would rather not do. It doesn't appear that any unusual software updates were made in the last 24 hours beyond Adobe Acrobat and Flash. There have been no system updates that I could identify within the last month or so.  Any suggestions?
Dell XPS 8300 - No Internet Access (Wired or Wireless Connections)