PC doesn't work (Sometimes)

[hoplessflower]

So basically,2 weeks ago,i tried to turn on my Pc as i do everyday. Everything went fine till i inserted a flash disk: it suddenly turned off. I tried to reboot it but only some parts of the pc(keyboard,mouse) worked,monitor without any signals. This for 2 days when i brought it to the technician but they couldn't find nothing: actually the first thought it was the gpu,and another one told me nothing was wrong,turning it on and off 15 times and every single one of them,the pc seemed to be working. I also changed my Power supply wire and it doesn't work either. What's the problem?

 

[NaderHussain]

What does the flash disk contain? Please provide some details regarding the flash disk's contents.

 

[hoplessflower]

its backup files since i formatted the pc for obvi reasons

 

[NaderHussain]

Ask the technician the reason he/she was able to turn on and off the computer 15 times without any problem. Also, find out if the external device drivers could be an issue.