Ok, you need to go to the Folder that contains your Lightroom Catalog. By default it is in Pictures and named Lightroom. In there you will find two items most likely - one is the catalog (ends in .lrcat) and one for previews (ends in Previews.lrdata), remove the .lrdata folder and you will be away.
New previews will need to be rendered and you can let Lightroom do this on the fly or you can force the rebuild. To do the later go to All Photographs (in Library/Grid mode) and select all. Then use the Build Standard Previews command under the Library>Previews dropdown Menu...
thx you very much! i got life in lightroom again!
If you ever need a bed in Amsterdam, glad to offer you one (lol)
All good Erik, have a happy Thursday....