|There is no CPU indicator led. There is one for power on, one for hard disk activity, and sometimes one for standby or sleep modes, which may be a third led or a different color of the same led as for power.|
Some computers will blink an led if something is wrong, or if the computer is in a Standby or Sleep mode.
If it is in a Standby or Sleep mode, if there is nothing wrong, usually moving the mouse or pressing a keyboard key will bring the computer out of that mode. If it is stuck in that mode, if there is nothing else wrong, usually holding the power switch in for 4 seconds or so will cause the computer to shut off, and you can press the power button normally after that to get it to boot normally.
If your neighbour has not been fiddling with anything inside the computer case, the two most common reasons a computer won't boot are the power supply has failed, or, less likely, the cpu has burned out from overheating.
Check the PS.
See response 4 in this: