I upgraded from 12.04 to 12.10 then on the same day to 13.04. The up-gradation happened successfully from 12.04 to 12.10 but while from 12.10 to 13.04 everything happened fine until the system got restarted. Unity is gone as well as not able to make any changes in the wallpaper, also most of the times the application gets stuck when I try to close it down. Trying to get icons display but am not able to. Tried using system settings but to no avail. Referred to the article Unity does not start in Ubuntu 13.04. But no changes in the system. Compiz is also not being very useful and does not do anything now. Need help. Thanks in advance for your thoughts. My systems configuration - core i5 2320 3.00 GHz 64 bits Architecture
It sounds to me like you did a messenger game upgrade. If so, you can backup your personal files and start over with a clean install.
First thing, did you use proprietary drivers? If so, you had to purge them before upgrading to don't experience issues, purging them now should solve the issue if this is the case.
If you didn't installed proprietary drivers you can try to re-install core packages that seem to be broken and reconfigure Xserver, assuming you have access to a terminal with internet connection, run these commands:
sudo apt-get update sudo apt-get install --reinstall ubuntu-desktop sudo apt-get install unity sudo apt-get install xserver-xgl sudo dpkg-reconfigure xserver-xorg
Now if your problem still persists you can try a last shot, reinstalling Xserver:
sudo apt-get install --reinstall xserver-xorg
If none of these worked, you'd better backup your files and do a clean install.