Windows Installer in Vista Not Working

Hi there. I recently upgraded my Dell Precision 690 pc to Windows Vista Business and now my Windows Installer doesn’t work. I understand that it is part of background services in Vista, and I have made sure it’s started, but I cannot install or un-install anything that uses it. I’ve posted inquiries to Winhelp Online Blog, which is moderated by Microsoft experts, but no one seems to know what to do. If you have encountered this problem and know the solution, I will be eternally grateful if you would share it with me. Thank you!