i downloaded a movie and now it wont play..help

You've tried the 'standard' troubleshooting e.g. closing the Videos app via the phone's taskbar, doing a soft-reset of the phone, and seeing if it then plays ?

If it doesn't then try deleting the film from the Videos app and redownload it via the Purchased tab in iTunes store app, or on your computer's iTunes and sync it back.

If the redownloaded copy also doesn't paly then try the 'report a problem' page to contact iTunes Support : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption