Snagit uninstalled itself

I have a new computer with Windows 7, so this may be a dumb question, sorry.  I recently installed the evaluation (30 day) version of Snagit version 11 which is supposed to work with Windows 7.  I had trouble during the install and only got it installed after I did two things - I right clicked on the c: drive and changed the permissions of the "Users" to Full control and modify, and secondly every time the install hung up (it would give a file name and say it could not find it or something like that) I would go to the folder mentioned in the error message and right-click and "take ownership".  I have installed something a co-worker gave me called "take ownership" - not sure what it does.  Anyway, a few days later I now go to use Snagit but the Techsmith folder is empty.  I ran the eval setup again and used the "modify" option and now I have Snagit again, but obviously I am doing something wrong.  How can I install Snagit and not have to run the setup program every day?  I am going to purchase it at the end of the trial (I have 27 days left).