ok, few things, what file type is it? Last night I started having a somewhat similar problem. I went to open a WMV file in FireFox and got an error message that the Windows Media Player Plug-In was not installed... but it was and had been using it, instead I tried downloading the file and then opening it directly with WMP but guess what WMP will not launch... no matter what I do. I would love to reinstall it but as far as I know there is no way to... except by reinstalling Vista... and its super annoying that you can only install the whole OS

GRRR you Microsoft, why do you do this to me? (tears)