Welcome to the forums Mick,
Are you trying to install a TBYB (trial version) or a full purchased version? There should not be any difference in the program itself. However I noted that you have downloaded it more than once, and the file name does not appear to be that of a TBYB. What size is your file?
When you get the message prompt that there's already an instance of the program/installer running, open task manager and look for it under applications or processes. You will probably find it under the processes. If you do, you can stop it. Then try to install it again.