Lenovo not starting up properly

Hi, my Lenovo was working fine last night but now is stuck on the pre-login page with dots going round in a circle. Has been doing this since yesterday morning. I've tried turning it on and off a few times, but makes no difference. Any suggestions appreciated!
 
Your post is confusing. First you say it was fine last night then next sentence you say "has been doing this since yesterday morning. ??? "
 
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