With ONLY I mean that when I push Pla! button the Uthgard emblem appears, the upgrading progress bar too, but thats it.

When the upgrading progress bar closes doesn't do anything else and you can't push the button again because you get an error telling 'You already have a game clent running blah blah blah'.

Tried to close ID account, close browser...etc...but the only thing it works is restart computer to be allowed to try Play! button again.

EDIT: rebooting the computer solves the problem, I'm giving info for a fix or a LESS drastic solution than rebooting computer thx.

You are lucky to only have to reboot. Sometimes It works but most of the times not. I have developed a ritual comprised of reinstalling launcher, re-logging, clearing cache, deleting user dat files, killing the .dll, restarting, trying other browsers... I will do that in various orders over and over again until it loads the game or I give up.

I don't know why they even went to this play button thing, its so stupid, the original launcher was way better, hate having to open up.

I'm currently having the problem now too, hate rebooting, so unnecessary but I guess they want that 2003 experience lol

The reasons are clearly outlined here: http://blog.uthgard.org/2016/06/why-play-button.html

The issue you are encountering is not related to the play button change at all btw., but due to a different change that adjusted the way the launching process works.