Some imported images in lightroom are greyed out. I've tried changing the colour management profile, update lightroom, remove preview file from the catalog folder and updated windows. Neither of these things make it work.
Some of the photos are greyed out and have an explanation mark, some are just greyed out. Selecting the greyed out photos results in a little symbol with the text "loading" next to "preset" to the right with no information shown while selected.
"...remove preview file from the catalog folder..."
This will result in the previews being 'greyed out' until the Catalog re-builds the preview cache images. You will need to wait. You could force the re-build (for selected previews) from the Menu: Library > Previews > Build.....
The previews with the exclamation mark [!] cannot be found by the catalog. They are "Missing". Previews cannot be re-built if LrC cannot find the original files.