I just had the same issue on Windows 10 after installing some plugins.
Cubase 9.5 shows the splash screen which then simply disappears.
Windows event viewer says:
Faulting application name: Cubase9.5.exe, version: 9.5.21.3, time stamp: 0x5ab3c490
Faulting module name: HALion 6.dll, version: 6.1.10.85, time stamp: 0x5ac4d406
I then simply renamed the “HALion 6.dll” to “HALion 6.dll.bak”:
c:\Program Files\Steinberg\VSTPlugins\HALion 6\HALion 6.dll.bak
Starting Cubase 9.5 then worked.
After this, I reinstalled HALion 6.1 (without the content) and then the latest HALion 6.1.10 Update (which was installed before).
Starting Cubase 9.5 then still worked.
The “HALion 6.dll” is the same as before. Strange, but anyway, this worked for me.
… but unfortunately, now it no longer works! Maybe Windows did cache the DLL somehow.
I have now replaced the “HALion 6.dll” version 6.1.10.85 with the older 6.1.0.72 version which solved the Cubase 9.5 start failure.
Hence, there seems to be a problem with the combination of Cubase9.5.exe version 9.5.21.3 and the “HALion 6.dll” version 6.1.10.85.
Checking the Windows event viewer if Cubase does not start seems to be a good advice for some cases.