Pretty sure there is more information to explain what it is you are trying to explain here...
That sounds like my sister trying to explain electronics to me..
PC.. The make model is?
Where and what was it or you doing when it shut down?
When it shuts down.. Yes the monitor will show no signal.
Pressing keys causes your numlock to blink. Willing to bet this is irrelevant.
Fans will do that when loading profile thru boot cycling.
At a lose here.. need better info...