@axel12 Sorry, i unfortunately haven't documented my enviroment variables before deleting... What i do know though is, that i had the following installed:
Java 8 Update 161 (64-bit)
Java 8 Update 191 (64-bit)
Java 8 SE Development Kit 8 Update 191 (64-bit)

And i had some JDBC entries in my enviroment that i deleted.

probably all not helpfull, sorry...

After succesively deleting everything Java SDK related from Windows (including the enviroment variables), reinstalling and restarting Windows it finally worked (following the advice given on a website that deals with an error that is related to this problem):

https://bugs.openjdk.java.net/browse/JDK-8231015

"CUSTOMER SUBMITTED WORKAROUND :
Uninstall other JDKs in the system. It seems removing the jdk 8 from the PATH env variable solves this."

I changed from 1.1.9 to 1.2.0 and have the same issue, tried all above solutions. The error log says the following:

Exception in thread "WindowsNativeRunloopThread" java.lang.NoSuchMethodError: <init>
at com.sun.glass.ui.win.WinApplication.staticScreen_getScreens(Native Method)
at com.sun.glass.ui.Screen.initScreens(Screen.java:412)
at com.sun.glass.ui.Application.lambda$run$1(Application.java:152)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:832)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.prism.d3d.D3DPipeline.getAdapterOrdinal(D3DPipeline.java:205)
at com.sun.javafx.tk.quantum.QuantumToolkit.assignScreensAdapters(QuantumToolkit.java:695)
at com.sun.javafx.tk.quantum.QuantumToolkit.runToolkit(QuantumToolkit.java:313)
at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$startup$10(QuantumToolkit.java:258)
at com.sun.glass.ui.Application.lambda$run$1(Application.java:153)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:832)

Any help is welcome!