Re: HELP! I think i lost all my data :(
Which is why I always recommend that when folks have two hard drives, and they want a different OS on each (Windows on one, Ubuntu on the other), they disconnect the Windows drive before attempting installation ...
You're best bet at this point is to boot from an Ubuntu LiveCD, go into Places, open the folders there for your MS Window partition, and see if there's anything there.
I've heard that you can then use Testdisk to recover your Windows files -- but I've never had any success doing that. I suggest you do a search in the forums for "data recovery" and look for threads where folks have used Testdisk on MS Windows partitions.
An alternative is to use an MS Windows-based data recovery product (which I always do with MS Windows partitions), but those cost money.
Ubuntu 16.04 Mate, Mint 18 Mate; MS Win 8.1, MS Win10 Pro.
Will not respond to PM requests for support -- use the forums.