ISTA suddenly "fails to start"

[bamboocha]

Hi there, 
i've been using some versions of ista for 5 years. Had been working quite well. 
I last used it a few month ago. 
Data had been on an external drive. 

Last weekend, i wanted to use it again. "ISTA FAILED TO START". sometimes the loading bar goes for like 40%; othertimes it doesn't move at all.

Since then I've been spending like 3 hours every day to uninstall, reinstall, clean the registry, uninstall with revouninstall, ccleaner, download other versions with "installers" from here. 4.3xx (old version)..from here.ISTA Standalone / SQLiteDBs / SDP / BLP - latest [TORRENT] with installer EASY. Also tried 4.52..

i have absolutly no idea why it suddenly stopped working. only thing i can think of is some update from windows 10?
I have like 50gb space free on the main SSD. 150gb on the external drive. i also tried installing ista on my NAS with a "Symlink" (CMD - MKLINK) So the PC thinks, data is on C while it is on Z (network) 

i've now orderd a bigger internal ssd (+512gb to install it here) an som ram storage (from 8 to 16gb)

do you have any idea what i could try??
thank you!