My default OS is out of boot options after installing Mageia

Hi guys !
So here's the problem;
I have installed Windows in sda ... then I have Linux Mint in sd2 ....and decided to install Mageia 4 in sd3.
Installation fine, except that my Linux Mint OS is not listed in boot options. So I'm stuck now because I made it my default OS.
Another "issue" ... terminal always return with " delaorden (my name) is not in sudoers list" !!??!!??!
I tried to add an entry from inside Mageia in boot configuration tool but failed.
Any help, please ?
Another question, please : which keys replace ctrl + alt + backspace in Mageia ... I use them to switch DE's or log out etc...
thanks in advance
P.S.: I'm affraid I picked up a non suitable distro for my knowledge. I can't even download a simple package... the message " please insert medium named Core relase..." what ??? I'm sorry guys, I'm leaving ... good luck. I just nedd something out of the box, like Linux Mint for example... now I'm going to format this sd3 partition and ask help to Mint comunity to recover my boot.
So here's the problem;
I have installed Windows in sda ... then I have Linux Mint in sd2 ....and decided to install Mageia 4 in sd3.
Installation fine, except that my Linux Mint OS is not listed in boot options. So I'm stuck now because I made it my default OS.
Another "issue" ... terminal always return with " delaorden (my name) is not in sudoers list" !!??!!??!
I tried to add an entry from inside Mageia in boot configuration tool but failed.
Any help, please ?
Another question, please : which keys replace ctrl + alt + backspace in Mageia ... I use them to switch DE's or log out etc...
thanks in advance
P.S.: I'm affraid I picked up a non suitable distro for my knowledge. I can't even download a simple package... the message " please insert medium named Core relase..." what ??? I'm sorry guys, I'm leaving ... good luck. I just nedd something out of the box, like Linux Mint for example... now I'm going to format this sd3 partition and ask help to Mint comunity to recover my boot.