It may be relevant to say that I am having many disk errors at boot of Windows10pro (v 1709, comp 16299.192). I can only log into the system after leaving the computer off for about 40 minutes. Once entering Windows, everything runs fine, and Chkdsk does not detect any disk problem, except that I can't do Avast scans without the button for this. I do not think it's a temperature problem since no overheating is indicated by the BIOS or softwares like Aida, Speecy, HDDThermometer.
My Avast version is 18.1.2326, build 18.1.3800.0, virus definition 4,192,553. If I do a clean install of Avast, I'll probably stay a long time without posting here because of startup errors and delays.