Does Strike show up as still being installed?
What if you check any/all Avid and Digidesign folders? is there any trace of Strike there?
Have you tried a 3rd party application like Ccleaner (for Mac) and check if Strike shows up as being installed? You can also repair permissions with Ccleaner (for Mac)
http://www.piriform.com/mac/ccleaner
Does your External drive contain a backup or something that may contain some Strike related files?
Maybe try unplugging the External and see if Strike will install.