Ok you may be furious but your problems are a faulty installation. I can only recommend that you remove all trace from your machine ,get a new download and reinstall. I recommend that when doing so you turn off all firewalls, virus checkers and if you have vista or win7 turn off UAC as well. Don't use Google Chrome to download, it nicks bits of code.
When installing always right click the icon and select 'run as administrator' I always use a 'Start up for complex aircraft' scenario to load the 757 into. I never have a problem and it flies well.
Good luck it's worth the effort.
David