Questions: Other

Greetings old friends. I'm super tired and the thought of explaining this properly is a lot, so apologies. 2000 characters disappering...

My bathroom exhaust fan was a bit noisier than usual when I turned it on today.
I figured I'd vacuum it, remove some dust. I've done this once before.

Told my husband, asked him 1. If he thought that white 'fluff' stuff might be mould, or if it was just dust (we both decided not mould), and 2. What brush he thought I should use. (He's way too into cleaning, and I am not, so I asked. Big mistake.

All I was asking for was advice. Instead, he took the entire fan housing out of the ceiling. To vacuum it. He unscrewed, unplugged.
When he finished and plugged it all back in, it was broken. Won't turn on.

Please advise what he did wrong. And fuck being democratic or pussyfooting around. Tell me straight. He's historically overconfident when it comes to repairs, especially with things electrical. He almost started an electrical fire before. He works in IT. He's arrogant about other skills like home repair.

He did not turn the breaker off when removing it, nor remove the timer switch piece.

Below the fan timer switch, there is a notch I noticed. It can be pulled out to deactivate the switch. He did not do this. The lights no longer come on, on the timer. We can compare it to the same model timer in our 2nd bathroom, which does have lights on permanently, even when not turned on.

He then completely removed the fan. He plugged it into a regular wall outlet, and it powers on. So, the fan is operational.
But when installed back into the ceiling, it receives no power.
He checked the outlet on the fan, and it shows no current, or not 120 V. It reads 0. xx.

Did he somehow fry the timer switch? How? Can we fix the problem by replacing the timer? We have the same model in the 2nd bathroom.

The fans are cheap, not more than $50, maybe. What I'm concerned about is he doesn't know what he did, and he may do it again, if we replace parts.