When I am trying to install Ubuntu(have it on a USB Drive), I am missing the 'Install alongside' option. Installer says 'This computer currently has no detected operating systems' though I have Windows 10 already installed. Tried using 'Something Else' option. It does not show any partitions. I have 5 partitions on Windows, it comes as single partition on Ubuntu installation. This is the first time I am trying Ubuntu. Please help.
Check and see if you are installing the UEFI or the legacy version (on the pendrive), as Windows 10 generally doesn't like to be installed alongside anything else.
If you're in UEFI (both Windows and the Pendrive version) then the install will detect both file systems. Optionally, you can turn off the UEFI in the Bios settings and select Legacy, but it would mean turning the legacy off (back to UEFI mode) each time you wanted to use windows.
USB Pendrive info: https://help.ubuntu.com/community/Installation/FromUSBStick
I have Windows 10 and Ubuntu Desktop 14.04.3 LTS installed on two machines(Desktop and laptop). Both are installed in EFI mode. In both cases secure boot in the BIOS is completely disabled. I have used this link
to create live USB. Changed the BIOS(from Windows 10) to boot to EFI USB(which contains Ubuntu Image). And it is working like charm. Make sure that your .iso image is not corrupt.