In the case of Guitar Pro 6 have you tried right clicking the Guitar Pro file and select open with? Then navigate to
C:\Program Files\Guitar Pro 6 if 32bit Windows or
C:\Program Files (x86)\Guitar Pro 6 if 64bit Windows
Select GuitarPro.exe this will set the files to open with Guitar Pro. Otherwise if it just will not open them for example freezes or has other issues, I recently had to remove and re install my copy of Guitar Pro 6 to fix a similar issue.