My PC locked up and rebooted itself. I had LR5 open and now when I bring it up it tells me it can't read from the previous cache and needs to quit.
Preview cache for that catalog has got corrupted.
You need to go to the location where your catalog is stored and get rid of the Previews.lrdata folder (not .lrcat file)
By default, it is located in Pictures\Lightroom
Retrieving data ...