Two days ago, the power button on my N9 stopped responding –pressing it did not lock the phone, and there was no tactile feedback at all.
I figured I’d just have to ensure that the battery never drained enough for the phone to switch off, and I’d be fine.

Today, the screen got stuck on the Settings screen. I can scroll up and down the page, but I cannot select any of the menu items. The swipe-from-top/side isn’t working and I cannot answer calls either.

So now, I cannot restart the phone, neither can I come out of the Settings page.

What. Can. I. Do?

What modifications have you done to the phone? Overclocking? N9quick tweaks, if so what tweaks? Does the phone respond to anything, and what have you tried?

Did pressing the power button for long time work??

You have to give more info

I doubt the power-button is the problem, the system just froze. Try to power it off and on again.

Try this thread for an advice on how to reboot the phone using Flasher. Whether or not it will help you depends on what else is wrong.

I haven't tweaked the phone at all.

The phone charges normally - I can see the charging indicator.

The power button doesn't respond at all, whether to long or to short presses; it feels as if the contact inside is broken.

The power button is certainly not the problem; but the fact that it isn't responding doesn't allow me to power the phone off.

I shall try that and let you know.. thanks.

Install app "reboot" to reboot the phone ?

Update:
The problem has resolved itself, without me doing anything.
I reached home, took the phone out of my pocket, and it was back to its normal, responsive self.

If anyone reading this thread came looking for a solution to a similar problem, I'm afraid I can't help you other than to say, "Let it sit in a corner for 6 hours."

That said, if anyone can throw some light on what can be done to prevent this problem in future/address this problem when it arises, it would be much appreciated. I'm in a country where Nokia has decided not to sell the N9, and I don't think I can get the power button fixed.. So I'd have to change from this otherwise-delightful phone if I can't do something to ensure that basic operations don't freeze unpredictably.

Do you have developer mode installed on the device?

If you do, then the easy solution is to ssh to your phone via USB or WLAN connection to see what's the problem and fix it.