I just did the upgrade to 9.1 and it will start and sit on the taskbar but there's no program window. I did an uninstall and reinstall (adding license) but the same thing happens. I have tried on two win 10 64 bit machines. Also, it seems you can't opt out when you hit cancel on the upgrade window. No way to launch the old version and now I don't have the program available at all.
I use Windows 10 64 bit too, had no trouble to install Jaikoz 9.1. and use it since the release date.
A hint from me: rename the folder C:\Program Files\Jthink and C:\Users\xyz\Jaikoz to Jaikoz_xyz and try to install Jaikoz again. You can do this procedure with every version of Jaikoz. In this way I have the new version 9.1 running and an older version as reserve.
using Jaikoz 9.4.1 NGS and as a backup Jaikoz 7.1.1
This is resolved. For some reason, Jaikoz was launching in a non-existent secondary monitor. I noticed that there was a minimized window when right clicking on the taskbar. On a hunch I connected a TV via HDMI and sure enough it was launching there. I closed that window and when I opened again it opened in the primary monitor. I had renamed the original install and did a "fresh" install and it was behaving this way consistently.