PC freezes or suddenly reboots? Hardware, rather than software problem.
In most cases, when there are hardware issues on the client side, the most difficult support task is to persuade a client to look for hardware problems.
Modern Windows operating systems are quite stable at least when standard hardware is involved and there are certain events that just do not occur on a hardware-"healthy" PC for the past five years. These include freeze when a mouse stops moving on the screen or unexpected reboots when a PC suddenly restarts without error messages. If you encounter these sorts of issues, there is almost certainly a hardware issue and you should look for it.