Why the computer error at certain places

This one of my experience too. I have repair the PC computer and finished, also the OS i have reinstalled.
The computer miner come and take home the PC computer. But after few hours He call me and say that the computer can't start and can't booting.
I say to him, please to take back to our workshop, so he come back with the PC. I try turn on the PC but not like he say, this computer normally.
And then i go to his home and check up the electrical source. and i get the problem f this condition, the electrical source have down and just 200Volt ( 220V normally ). So the problem not the computer but the electrical source. This condition finished by Electrical engineering and solved.