I have had no bigger problems earlier with X3 but now I can't get it to open. I haven't done any changes that I know of since yesterday that 'm aware of. When I start X3 the icon shows up down on the screen, the blue square that informs how many plugins I have shows too, but at the desktop no program is shown. It's like the program is minimized. I've tried to restart computer, start X3 from Startmenu (and start with a specific song), running it as administrator. All I can think of now is download the upgrade X3C again and re-upgrade it, but it will take over 1h download time. And I feel that it can be solved with an stupidly easy step so therefore I ask about some help here. =) If I reinstall/re-upgrade, do I have to remove X3 before that? I really don´t want to loose my new settings... btw other progs are working and opening fine.

Have you gotten any updates for windows since yesterday. You should bring your computer back to an earlier date when sonar worked and try from there. That would give you more information.

Thanks Cowboydan, I look into that.

You shouldn't have to download X3c again, simply re-run the file you originally downloaded.
 
Right click it and choose "Run As Administrator"

I deleted it. I'll try that in 28 minutes!

I tried to reupdate X3c, no effect. I then backed the date to two days ago, then it worked (thx again cowboydan)! The only thing I have seen installed since then is a Windows Defender update.

Since the splash screen and plugin scan are showing up this sounds like your primary window is open but off screen. I've seen this happen and I forget the key strokes. However doing a search in Google for "move offscreen window" got me to this answer:
 
[select the icon on the task bar] and hold down the Windows key and press the right-arrow [or left] a few times. That should move the window across your screens and eventually bring it back onto the screen that is still active.
 
Regards,

Thanks for your answer mmorgan, this could probably have been the case. I will remember it and try this if its happen again!