It seems that some people automatically assume that they should enjoy a "classic" because they have been told it is essential reading...They are not classics because they were the equivalent of our Harry Potter, with characters and story lines which really attempt to appeal to the reader in a conventional way, but they were novels which broke free of expectation, resisted ideals which may or may not still exist in our contemporary world and reflected their own societies in new and daring ways.
So perhaps instead of wondering why you can't like a book, attempt to understand the time it was written and the reasons behind writing it, as well as why it may still be enjoyed today.
I hated Tristram Shandy by Laurence Sterne. Whilst reading it I just couldn't get into it at all. It wasn't until after talking to others about the book, and hearing why it was such an important piece of writing that I began to understand why it may be enjoyed. However I still didn't love it myself. So if you can't come away from a classic with any enjoyment, I think it is important to understand why it's a classic. That way you aren't left thinking your just a little strange for not 'getting' a book.