Ubuntu 15.10 not booting

[ddube95]

I upgraded ubuntu 14.04 to 15.10 successfully.
Then I tried cleaning up old files using Ubuntu Tweak and something went wrong, as I cannot boot my system anymore.
I downloaded boot repair tools which reported success, but the system still does not boot.
I have uploaded the boot info at http://paste.ubuntu.com/13856984 and http://paste.ubuntu.com/13857155
Please anybody help?
Thank you very much.

[john492]

did you install Ubuntu Desktop during installation?

[grahammechanical]

What is the Grub error message? Does Grub go to grub rescue? Did you use Ubuntu Tweak to remove previous kernels? Did you remove all the kernels?

[ddube95]

When I boot the machine, the error says "Operating system not found".
I was removing old kernels. I do not know if I removed the newest kernel?

[ddube95]

P/S. I installed Ubuntu desktop