So this is a late post, and the original post owner has probably fixed the problem but for anyone else reading this forum:
I had the same problem, opened for a second and then closed revealing nothing but theme music and if i used my mouse over the icon on my task bar, it would just show x, enlarge/decrease screen size and minimize. Clicking on i would not solve the problem.
I’m not sure what caused the problem as i didn’t play around with any files.
HOW TO SOLVE:
what worked for me is simply uninstalling using windows search “uninstall a program” and then simply re-installing. Yes the process takes a few hours but it fixed the problem for me. definitely worth a try if you are running out of options..
I hope this helped and good luck solving your problems with gw2 to get it running again