What? Are we supposed to just guess at how distorted it is? A screenshot would really help.
I agree with Jim that we need a screenshot.
Here are a couple of things to try
1. Zoom in and out
2 if that didn't help than with one distorted photo selected in the filmstrip try menu Library/Previews/Build Standard Size Previews and in the dialog select Build Selected. If this works your preview cache is probably corrupted.