Might be the display profile. Try switching to a sRGB profile and see if that helps.
The previews cache may have become corrupt.
Go to your Lightroom named catalog folder (usually in Pictures by default) and inside you should find the catalog (.lrcat file) and a folder ending previews.lrdata
Don’t touch the .lrcat file but delete the previews folder or rename it.
Re-launch Lightroom and that should force the previews to be re-generated.
If that doesn’t work you may need to adjust your monitor profile.
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Thanks for your input. Tried this but it didn't make a difference. Switched to a different sRGB profile did work.
Glad to hear everything is working again after re-setting the default display profile. Thanks for letting us know.