It's me here again, yay!
Okay, here is the deal. My old computer had been crashing few months back, so I sent it to warranty repair, it being package computer and all. They told me that the motherboard was broken and they changed it, np, no more bluescreens or weird errors. Since then I have bought new computer (in parts this time!), and gave the old one to local company for office use. They ran some tests of their own and reported to me that the computer was infested with viruses of some sort, and that was the reason for the crashes. What boggles me here is that I never ever had any viruses on the computer before or after repair, at least according to weekly full scans with Malwarebytes and Avast, both of them. I never encountered any suspicious slowdowns either.
So I am asking here, what are the odds having a computer infested with viruses and Avast OR Malwarebytes not detecting it, and not suffering from any slowdowns?