Movies hav e disappeared from my iTunes [for Windows] library; can

Last week, sizable number of movies have disappeared from my iTunes library. In a couple of cases, they are movies I watched within the last month.

When I look at my movie library listing, I see the title, and a gray box with an image of a frame of film -- it would normally display the movie artwork. Here's one example:

When I check iTunes >> iTunes Media >> Movies, there is no folder for the movie. I can't figure out where the library listing is finding the movie title to display it.

When I go to the store to try and download a replacement copy, my only option is to purchase a new copy.

I have checked on a few of the movies in my past purchases. I've found order numbers for each of the movies I've checked.

My first concern is how can I access/download the missing movies?

Secondly, why/how did they disappear in the first place?

The first purchases in my library were made in 2011. I have used iTunes for Windows exclusively to manage my library.

The purchases have been made from six different computers; each had a different name.

tia for any help you can offer yto rerstore the missing movies.

mm