PeteCresswell wrote:

PC is spending most of it's time at 100% CPU, but the heavy hitter seems
to be hiding in SVCHOST.

viz: http://tinyurl.com/jyr7l3l

Response time was (and still is) at a crawl.

Ran MalwareBytes and removed a couple of bad actors, ran the Norton
uninstall for Comcast's competing anti-virus (Avast already installed).

Rebooted, at first it seemed to be better - but then back to 100% except
that something called "TrustedInstaller" was the heavy hitter for a few
minutes... and then it was back to SVCHOST.

Looks like TrustedInstaller is a legitimate Windows system app that,
among other things, is a player in WindowsUpdate.

Unencumbered by any knowledge or much grey matter, I would theorize that
somebody has managed to inadvertently install something that doesn't
want to die or be killed off.

But what?

Anybody else been here ?

Windows Vista Home Premium, SP2, 32-bit
AMD Athlon LE-11620 @2.4 GHz w/2GB of RAM

Might it be time to cave in and "Upgrade" to Windows 10?
Or would that be jumping from the frying pan into the fire
w/only 2 gigs of RAM and that rather old CPU?

If you don't need them anymore or right now, does disabling System
Restore help? You did not say what type of disk you have: HDD or SSD.
System Restore can cause heavy slowdown on SSDs.