Cubase 11.0.4 has gone wacko

Hi, my Cubase 11.0.4 has just stopped audio, creates the fuzzy old low latancy fuzz. I have reinstalled it, gone back a few steps and it still isn’t working. This has just happened.
Cubase Pro 11., Scarlet 4i4, SSD’s, MSI quad, 32G Ram, Win 10. I have pulled out all inserts and the problem is still there. Premier CC, Reason etc., doesnt have a problem. Any ideas please
Cheers … Akasha