With the power to that light turned off at the circuit breaker box, try
cleaning the contacts in the socket (where the bulb screws in and makes
contact). Use sandpaper.

Yes, thank you.. that is what I meant. I didn't know what the thing was
called that you put the bulb into!
I'll tell him and we'll try that, thank you,

TURN THE POWER OFF IF YOU DO THIS!!! Not just via the switch, but at
the circuit breaker.

That's what I said, but it bears repeating.

Also, in general I would say that if electricity mystifies you, you should
get professional help.