have you got the pinnacle 17 running on the same computer as the 18 ?
they may be conflicting or the 17 does not get completely uninstalled and the 18 cant overwrite some of the files that they both use and it pulls up the wrong version and crashes
try uninstalling both versions using the revo uninstaller on this page.
you can use the free version on the left. no need to even take the trial offer for the pro
after they are both uninstalled completely
re install the 18 by right clicking on the setup file and selecting
run as administrator.
let me know if that works please.