I held power button for minute and flasher didn't found the phone.
As far as I remember usb icon should appear immediately when phone turns on after I connect it to PC.
But now it doesn't happen, phone boots up like it does not connected to usb and it reboots when the circles around Nokia logo appears.
Flasher (no matter what arguments I use) also does not detect the phone.

I will try on another PC and another usb cable, but I am pretty sure that problem in a phone.

One more interesting thing: Alarm still works.
The phone was turned off, but it the morning it woke me up with alarm, as usual.
I forgot that N9 is dead and turned alarm of, then I realize whats happened. Phone stiil won't boot up, but alarm works O_o
I want to try to flash it with Phoenix, but I stuck with "phoenix neither dp 1.0 nor dp2.0 was found for the product' error. Looks like it doesn't detect the firmware even if I put it to the Phoenix directory, including \Phoenix\Products\RM-696\

I managed to pass Phoenix "neither dp1.0 nor dp2.0 was found for the product" stage and I have found that it doesn't detect phone too.
Device Manager doesn't detect any device as I connect N9 to USB.
Looks like there is some kind of short circuit in USB port of N9 which makes it think it is already connected to PC at the same time as it doesn't want to connect to PC. Sort of.