I have started upgrade form 7.13.0 to 7.14.2

As a result, hap AC^2 could not start anymore

Reset not work

Netinstall also not work

Netinstall does work in vast majority of cases. But it's a very fragile process (a bit less so if using linux netinstall) so it may take some (or many) tries to make evrything click together.

Used linux netinstall-cli

netinstall-cli shows Waiting for ROUTERBOARD

1. Disconnected all
2. Press reset
3. Plug power
4. Waited till usr stoped blink
5. Put ethternet cable to 1st (WAN) port

nothing

The port that you should NOT (normally) use for netinstall Winbox is ether1 (or anyway WAN ports) try one of ether2+.
See:
viewtopic.php?t=206301

EDIT: Sorry for the confusion, for netinstall it should be the "boot" port, which is usually ether1.

Try these steps:

1. Disconnect everything
2. Start netinstall on linux machine
3. Connect ethernet cable brtween PC and ether1
4. Press reset and keep pressing it until step #6
5. Plug in power plug
6. When netinstall executable on linux machine detects hAP ac2, release reset button

The port that you should NOT (normally) use for netinstall is ether1 (or anyway WAN ports) try one of ether2+.
See:
viewtopic.php?t=206301

Wrong. Netinstall is always done via ether1 (which is usually WAN port) ... and this includes devices with single (management) ether port.
You're right about using any port except ether1 for configuring (after netinstall finishes). Except for devices with management ether port.

I'm 100% sure that ether1 is the right one on hAP ac2, I did netinstall on my hAP ac2 3 times so far. Successfully every time and have used ether1 every time.

My bad, I was thinking of Winbox.

Solution found in this server - disable firewall (in my case ufw) before starting netinstall-cli as it blocks PXE server (maybe it is possible to write some rule for ufw, but I have no time for this exercise)