answer:Umm, if you really installed it in Virtualbox then it can not launch when you start the computer because you would have to run Virtualbox in Windows first to launch Ubuntu. So there are 3 possibilities. 1. You somehow only suspended/hibernated the machine and resumed into a full screen mode within Virtualbox. In that case, make sure you really shut down ubuntu. If 1. is true, the virtualbox window should close. 2. You installed Ubuntu not inside Virtualbox but on your machine, and created a dual boot environment. Restart your machine and watch the boot process. During boot, you should be prompted to select which OS you want to start. Select Windows when the choice is presented. 3. You installed Ubuntu on your physical machine and replaced your windows entirely. You are pretty much fucked. If you are lucky, windows folders might still be present in the file system. Copy the files you want to back up to a different partition/drive and then reinstall windows. 1. is the least likely of the 3, 2. is the most likely.