Problem formatting time from an XML Document

Hi All,
I received an XML document that was downloaded from FilmFreeway (a film festival registering site) which contains a list of all the films and their durations for the film festival I'm programming. I have opened it in excel and saved it as an excel worksheet to manipulate it.
It appeared to be normal, but I cannot get the Duration column to sum the duration of the film times using a sum formula. I've tried reformatted the Duration column cells using [h]:mm:ss but that doesn't help either. I've tried copying and pasting the values from the Duration cells to new cells and reformatting, but to no avail. The only thing that works is manually retyping each cell out and then using the formatting [h]:mm:ss. Once I do that I can sum the times. But I really don't want to go through all the hundreds of entries and retype each one -- there's always the chance for a typo then. I'm attaching a bit of the spreadsheet for your viewing pleasure.

The only thing I can think of is that whatever format it was downloaded and given to me (I think comma delimited) has done something weird to the Duration column. If you find an answer to this problem, please let me know! In the mean time, I'll be slowly going through and retyping all the film durations into my spreadsheet.
Cheers,
K-