System freez on shutdown

[vsmmath]

Installed 16.04 on Intel LGA775 motherboard, 3 GHz D, 2Gib DDR2, 250 GB WD HD.

Everything is working fine. I have updated and upgraded before installing some software. Python is installed. VLC, Sakis3g and SMS tools are installed.

When I shut down the system, system freezes at Kubuntu display. I left it like that and went to get ready for bed, say 10 minutes. When I come back I see that nothing is happening. I have to switch off the system.

Is this because some application is running in the background and has not shut down. I was working at the command prompt and gave exit. Disconnected Internet before shut down.

Any possible reasons.

[vsmmath]

I think I found what is the problem.

My power supply gave problem and I purchased a SMPS locally. What they sell in a small town is may be 300 Watts when I was told it will be 500 Watts. When I found out that SMPS is no good, I searched in my junk yard I found two 550 Watts SMPS PowerSafe. These were purchased almost 12 years back and all the wires were eaten away by mice. I took one out cleaned and opening my new power supply took all connecting cables and fixed it in the old SMPS. From the afternoon I am not havening that freeze problem and the fan noise is also reduced. I just wanted to inform what bad SMPS can do to a system.