Question: Trying to open file - TEXT FORMAT CHOICE - please help

I am having issues opening my final year project, it was working an hour ago and now it will not open. When I try to open the file it brings up a box title TEXT FORMAT CHOICE with the options: MAPLE TEXT, PLAIN TEXT, MAPLE INPUT and CANCEL.

This is all my work and I need it to complete my year.

Any help with how I can rectify this would be extremely helpful.

Many thanks

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