I want to dual boot my laptop(lenovo G580). It currently has windows 8.1(unactivated). Now I also want to install ubuntu 14.04 64-bit, so basically I was trying to dual boot using bootable usb drive. When I first try booting ubuntu, in the process, it says no previous OS installed i.e., its not recognizing windows 8.1, so I search google and somewhere found that I need to disable UEFI mode. After disabling UEFI mode I again tried to install ubuntu, but this time the usb stick is not getting recognized(or OS inside is not getting recognized, bcoz the boot manager recognizes HDD and tries to boot from it) and this below statement on a black screen comes out and then nothing happened.
"An operating system wasn't found. Try disconnecting any drives that don't contain an operating system.
Press any key to restart. "
Please some one help I want to install ubuntu over windows. Also, please do tell me if any other info is required!