On 16.04, PC always goes to sleep at random time after boot splash and during login screen.

Ever since I upgraded to 16.04 from 14.04, PC always goes to sleep at random time after boot splash and during login screen, mostly happened right after splash is finished, screen turns black, then PC goes to sleep, but it can also happen while typing password in login screen. The same thing also happened on fresh installation.

I don't know which package caused this, it never happened on 14.04 and previous LTS release.

1) Description: Ubuntu 16.04 LTS Release: 16.04
2) I don't know which package caused this
3) After booting up PC should wait at login screen until I entered password and logged in
4) After booting up PC goes to sleep immediately, there is no way to prevent this, even if I moved the pointer or even while typing the password.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.14
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon Jun 6 23:31:15 2016
InstallationDate: Installed on 2016-06-06 (0 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)