another reason could be due to anti spyware program u install like adware. during installation, premier pro will edit some of ur registry keys. with those anti spyware program install, it will prevent premiere from doin so. u might not notice it but after the installation, u would hav problem opening the software.to solve the problem, simply uninstall premiere pro first. then close the spyware program and install premiere pro. once installation is done, then enable ur spyware back again