NAT, etc also didn't work for some odd/unexplained reason.
Then I reinstalled Virtualbox without bridged network, and I noticed the registry key was deleted (probably by Virtualbox setup), and the "Virtual Box Bridged Networking Driver Miniport" disappeared from device manager. I uninstalled VB and reinstalled it again, with Bridged support, and voilà, everything is back to normal.The common trend seems to be the loss of Windows 8.1 gateway information in both scenarios. Furthermore, the uninstall will NOT remove Virtualbox ethernet adapter, and you can't able to remove it manually (but at least the internet connection come back).Edit-To supply additional info: Do you have any custom networking-related software installed on your win8.1 host? antivirus/firewall/VPN slient/other hypervisors/etc. EDIT: On reinstall Virtualbox install one more Ethernet adapter, it not use the old one, and still can't delete the adapters.Ok, I was able to fix my problem, here is what I did.I noticed that I had many network cards labeled "Virtual Box Bridged Networking Driver Miniport" with a yellow exclamation mark, remaining in Windows Device Manager, but impossible to delete them.The connection will not get dhcp until I disabled the "Virtualbox bridged networking driver" in the connection properties.As soon as I do that, I can bring the connection down and back up with out issue and then enable the driver again and all works.PS : I also ran /scannnow to detect any possible error in Windows, but it didn't found anything, and I don't think it helped to solve the issue.Franck, So far, this is my observation based on my experience. Unfortunately, now that it is fixed (partly, see below), I can't reproduce the issue, but I tried to be as precise as I could in my resolution decription.If you try to go backwards to 4.2.14, the drivers are still gone. In Ubuntu, the WLan0 is available but does not work correctly. I haven't checked it on Mac yet, I don't have it available to use.I uninstalled and went back to version 4.2.6 in windows and virtual box drivers will not load or work. Where are the drivers located so the files can be removed? We did a clean install of Windows 8.1pro and installed/used Virtual Box 4.2.14/16 with a virtual Windows 7 environment which worked for awhile, then the network connectivity would be lost in Windows 8.1.