Installed Ubuntu 16.04 on a Windows 8.1. At first only windows booted up, so i try the Boot-repair tool 2 times, after boot repair, i have a message like RESTART AND SELECT YOUR SYSTEM OR INSERT CORRECT MEDIA AND PRESS ANY KEY. None changed aftter 2nd repair. Then i reinstalled all the Ubuntu package, none changed. Is first time for me that have touch with Ubuntu or any linux system (Only Windows).
Check your UEFI settings in BIOS. UEFI will usually make it impossible to dual boot in any scenario.
If your UEFI is already disabled, try changing the secure boot setting and turn it off.
Doing this should help you. It did for me and I'm currently typing this on an ASUS X550LA that is dual booting to win 7.
Also, considering that you already reinstalled Ubuntu, and still nothing changed, you may have to reinstall Ubuntu again to get the GRUB selection screen to work properly. I think that UEFI/secure boot may be overwriting the GRUB overlay, thus preventing you from getting into your install.
Thanks Mr Claycomb and WinEunuuchs2Unix, UEFI is not disabled, but secure boot was before the first installation, with it there was no way to boot from cd. Both systems are installed on UEFI settings. Turning off UEFI do not make the things worst? Hardware is ACER Inspire M3985, Corei7-3770, BIOS ver P11-A0
By the way, When installed Ubuntu, i shrink windows partition from windows to free some 65GB, turned UEFIs Secureboot off, and changed boot priorities to remobable media first, second the cd/dvd driver, third HDD, and fourth LAN. Booted up from Ubuntu DVD, and installed. HDD Partitioning automatic, the installed used 5GB for SWAP(sda10), and the rest 60GB for Linux File System (sda9), 2nd time i used the option of remove the old one and install.