Today, Mehrnoosh brought her PC to the company and asked me to take a look at it. She said, she can not turn her PC on anymore.
The first thing I did was plugging it to electricity and making sure its power cord is OK! Then opened the case doors and detached power supply unit connectors from motherboard, HDD and ODD. Then tried to connect green wire to black wire via a jumper to make sure power button is not the problem. I realized power supply is not going to be turned on by connecting green wire to black ones. So, power supply is damaged (it’s possible that power button has problem too). We completely detached power supply and replaced it by a spare power supply. Everything was OK and operating system was booted. So, the only problem was the power supply itself. As, I know by experience, a lot of power supply makers use poor capacitors in their products, so they will blow up after a few years of working.
I opened the power supply ans saw I was right! Some of capacitors were blew up!
The main problem was related to a 10 volt/2200 micro Farad capacitor, so I suggested Mehrnoosh to replace it with a 16 volt or more, same capacity electrolytic (preferably, solid) capacitor or buy a reliable PSU like Cooler Master products. She chose the second option!