First, make sure that the file you are trying to open has the file extension "ptb".
Second, if this is the case, go to the directory that contains you want to open, right click on it, and select "Open with...".
See if "Power Tab Editor" is selected as the Recommended Program. If it is listed, selected. If it is not, then click the "Browse" button,
and go to the directory where Power Tab is installed, and select the file PTeditor.exe. By default, the program installs to:
Program Files (x86)/Power Tab Software/ Power Tab Editor 1.7/PTeditor.exe.
If you have "Always use the selected program to open this kind of file" checked, then Power Tab should open these tabs automatically now.