Hi wlewarski,
As my last post says, I fixed the problem with a format/re-install but out of curiosity I followed your links in case it ever happened again....... search, run, regedit.exe, hkey_local_machine\software\policies\microsoft\.....then all that pops up are cryptography, peernet, system certificates, windows, windows NT. No windows defender appears?? Don't know what, if and why but defender is working fine now. Anyway, thanks for your input.