The movie I downloaded does not play, how can i get my money back

Delete it and redownload it:

Open the iTunes app > More > Purchased > Movies

If this is on your iPad then you've tried closing the Videos app via the taskbar : from the home screen (i.e. not with the Videos app 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of the Videos app to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.

And/or tried a soft-reset : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.

If neither of those work, then depending upon what country that you are in (films can't be re-downloaded in all countries) then try deleting the filme from the Videos app and redownload it via the Purchased tab in the iTunes store app.

If you aren't in a country where you can re-download films or if it re-downloads with the same problem then try the 'report a problem' link from your purchase history : log into your account on your computer's iTunes via the Store > View Account menu option and you should then see a Purchase History section with a 'see all' link to the right of it ; click on that and you should see a list of your purchases ; find that film and use the 'Report a Problem' link and fill in details about the problem (iTunes support should reply within, I think, about 24 hours).

If the 'report a problem' link doesn't work (it's been taking some people to this site on a browser instead of showing a form in iTunes) then 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.