Can anyone help me with this problem? I've have no idea what to do about this problem!
Locate the folder with your catalog and previews (by default in Pictures) and delete the Previews.lrdata folder (with Lightroom closed).
You will need to rebuild previews which can be done as you work or by going to the All Photographs Collection, selecting all and from the Library Dropdown Menu selected Rebuild Standard or 1:1 previews...
Thank you very much Geoff! it is finally working Again! what should i have done without you kind people, thanks Again you made my day!!