Sounds like the Windows Update Service might be the problem, have had this myself on two different laptops and there are many posts about it on the net.
Try going into run then services.msc and scroll down to Windows Update Service, right - click, properties and set to disabled. (also select to stop service) The issue is that when checking for updates in the background it will very quickly use up 100% of the CPU (or 100% of one core if multicore) which on a single core machine grinds it to a total halt.
If that stops the problem then you have a choice of leaving it disabled (no updates = increased risk) or trying leaving it on for up to 48 hours or more to maybe sort itself out.
Some have speculated that Microsoft did this on purpose to get people to upgrade to W10......