Why Does the Programme Keep Crashing?

Every time I try and move a book over from digital editions onto my ereader, the programme crashes and it doesn't work.  This is a new issue so it is not a compatibility issue or anything like that.

I download the books from waterstones website, open them in digital editions and then when I try to move them over, it just crashes.

I do have an error message keep appearing when I open the programme saying something about corrupt/unreadable files and to check the chkdsk utility.  I have no idea what this is and it is getting very annoying.  So far has taken me 5 hours to transfer 2 books.

Please help

p.s this has happened on versions 3, 4 and 4.5