Re: Windows 8
I doubt if Windows 8 is the cause,it is more of a victim of circumstance. I would say though, that it happened to come along at the same time as a major recession, at a time when tablets and smart phones were reaching maturity and in which the non-power users realised that a PC was overkill in relation to their real needs.
W8 is also on the, "I hate Windows Cycle" ( every second version) and it was developed for touch screens so it shouldn't really have any influence over the non touch screen market.
Business is also extending refresh from 3 years to 4 years for financial reasons, PCs now have far more power than office workers require, XP is still fine for business, so there are fewer reasons to upgrade ( that's what the bean counters want anyway).
PC sales are failing because there has been a paradigm shift in what users currently use/require. It's called evolution.