are you by any chance using comodo antivirus? if yes, then try this: https://forum.4game.com/showthread.php?t=1272 .
i have a simillar issue, can't go past the update button (i have no antivirus, and windows firewal is disabled), also, i played well untill 2 or 3 hours ago, but the game crashed (i closed l2.exe on task manager) and wasn't able to open the game after that.... ended up reinstalling 4game couple of times and now all i got is "update" button over and over again, and it doesn't seem to be updating anything...
good day, you can see actual solutions and issues' statuses here. additional instructions could be found here. if you can't find a solution for your issue you always can ask for moving the thread back into the main branch. best regards