I hate these problems, I really do. I worked at a computer retailer for nearly ten years, and we had plenty of these cases. I always found that most of them were something at home with the user, and it is usually network- or power-related.
The best advice I can give is trying multiple things, even if they sound ridiculous. Here's a list:
- Connect only the keyboard, mouse and monitor - disconnect everything else (speakers, USB devices, etc).
- Completely disconnect from the Internet, through Wi-Fi or ethernet.
- If you're connected through an ethernet cable - change this cable.
- If you're connected through an ethernet cable - disconnect the cable completely.
- Try a different power board, or plug it directly into the wall.
The system must be okay if the computer technician had it working, where at home it's not working. Try turn off all other computers in the house, desktops or notebooks. Turn off all Wi-Fi devices, tablets, consoles, smartphones, baby monitors, etc. Eliminate everything so your PC is the only thing on and connected to the network and go from there - eliminating options as you go.
It could be a conflict on the network, a virus, malware - something hitting your computer from another computer. The best advice is just going back to basics - disconnect everything and get it to work, then one-by-one start connecting everything and see what is causing the fault.
I hope you get this sorted!