From yesterday onwards when Ubuntu starts my system shows following error message:
Starting redis-server: redis-server.
speech dispatcher disabled; edit /etc/default/speech-dispatcher
* Starting vnStat daemon vnstatd [ OK ]
saned disabled; edit /etc/default/saned
* Starting web server apache2
apache2: Could not reliably determine the server's fully qualified domain name,
using 127.0.1.1 for ServerName
[ OK ]
* Checking battery state... [ OK ]
* Starting TiMidity++ ALSA midi emulation... [ OK ]
Sometimes Ubuntu loads properly. Even though it loads properly after some time it freezes and next time onwards the same black error screen appears. Each time this error occurs the boot screen color also changes and some horizontal lines appear on the screen.