I bought a PC with Windows 10 on it, which has a SSD and HDD drive. I attempted to create a multi-boot setup with Windows 10 and Ubuntu 14.04 (the Windows folder is on the SSD, and I wanted the Ubuntu partitions to be on the HDD drive). I tried several times to set up dual-boot (with Ubuntu 15.04, 14.04, Mint 17.3), with no success.
Then I found this suggestion here https://askubuntu.com/questions/339687/dual-boot-goes-to-win8-doesnt-even-show-grub-screen that said to run boot-repair from a Ubuntu LiveCD ( I realise the problem there was different from mine, so I see now this was probably very stupid). Following that, my PC now always boots into UEFI. When I then exit UEFI, the screen goes black for a second and goes straight again into UEFI. The exception is if I press F8 during booting to go into safe boot, then it actually boots properly. I found that after running boot-repair, I now have a efi/ubuntu/shimx64.efi file on the HDD disk as well. (I already tried resetting everything I changed in the UEFI -secureboot, faststartup, etc. - to its defaults)
I would be happy for now with getting my computer to work properly without dual-boot, I don't have much data/many programs on this PC (all backed up as well), and I have the Windows License Key and a Repair Disk to reinstall Windows, so instead of looking for the error and breaking even more I'm considering simply doing a re-install of Windows from the repair disk, with it deleting all the data on the PC, instead of looking for the actual problem.
Would a full reinstall of the OS solve my problem and get rid of the linux distro I seem to have installed, but which is not working? Is there a chance it could cause even more problems? Obviously I'm thankful for other suggestions as well, I just want to be sure not to break it further :)