This is probably caused by a defective monitor profile, although it could also be a corrupted preview cache.
Since this is happening from the start with a fresh install, I'm guessing that it's the monitor profile.
Lightroom is color managed, and depends on a sound and correct monitor profile to display images correctly.
Go to Control panel > Color management, and set the monitor profile to sRGB.
If this fixes the problem, you should ideally calibrate your monitor with a hardware calibrator, which will create a new profile that accurately describes your monitor.
Well, thank you Per,
I didn't look at the colour settings because Photoshop works fine.
Anyhow, your suggestion fixed my problem.
Ligthroom is particularly picky about the monitor profile, and a profile that works with Photoshop can create problems in Lightroom.
Blank previews is only one of the symptoms of a defective profile, others include a brownish yellow cast in the images (which also shows in the neutral gray areas of the histogram), and different colors in Library and Develop.
Using sRGB as the monitor profile works, because most monitors have a color gamut close to sRGB. But it will not be entirely accurate, so it is always best to calibrate with a hardware calibrator, which also creates an accurate profile.
If you have a wide gamut monitor, you should use Adobe RGB instead of sRGB, but most laptops don't have wide gamut screens.