Elizabeth is having an issue with her Apple iMac rebooting randomly. Leo says that overheating may be the culprit. Computers will shut down or reboot when it overheats. But if it happens when she's doing nothing, then overheating is unlikely. A buggy operating system may cause it if a process is running away. It could also be a power issue in her home. Power can be "dirty" and that could be causing it. Using an uninterruptible power supply (UPS) could prevent low power and power surges. The electrical cord being frayed and loose could cause this too. It may also be a failing power supply.
Another solution could be to try and plug it into a different outlet.