Download Prompt - In IE, Trusted Intranet - just started

Hey guys, I am having an issue.

Running 2010 Farm, 1 App 2 Front Ends 1 SQL

For some reason this morning whenever anyone goes to any document lib or any link to a file they are greeted with a download Prompt asking them to either Open, Save or Save as..

Not sure why this started or how to fix it.

Everything should open in client side apps, office 13.

All Lib Settings are set to open in Client App done at parent lvl for all sites.

Any ideas would be helpful, just spun all server and still same issue.

Boss is raged, I am grateful for any help. Thanks guys.