Through alot of add-ons and liveries, i have somehow done something terrible to the default 747 files. Anyway when I select a default 747 I get an error

Try this,1. Move the 747 aircraft folder away from the FSX folders.2. Run a repair install of FSX. All missing files should be reinstalled.

so that is what a repair install is?replaces anything missing from the original install?if so that is brilliant, means i dont have to re-install my scenery and other planes etcwill give this a shot - thanks UlfB