After earlier problems with a dual boot setup with windows 7 and ubuntu 14.04 I decided to start with a clean install of windows 8.1 and installed ubuntu after that. After the installation of Ubuntu (from live-usb) on a new partion my computer (HP Elitebook 8570W) only booted windows 8.1 without letting me choose. Therefore, I decided to run Boot Repair by using the ubuntu live-usb. See Boot Repair boot info summary. However, when starting up my computer it gives an error saying "BootDevice Not Found" and "Hard Disk - (3F0)". I'm quite new to ubuntu and don't know a lot about bootdevices etc. Any help is very much appreciated.
It is not the smartest answer, but you may solve it with Easy BCD. It's a tool used to modify the booting options. Download it to Windows 8, install it and there you will get the option to modify Windows boot by adding Ubuntu to boot list. Despite It worked for me, later on I decided to uninstall Windows 8.1 cause It made Ubuntu to boot unproperly (in my case).