Harry Bloomfield brought next idea :
Just to recap - Over past few weeks my W10 Acer laptop had more and more
frequently locked up, no mouse movement, no response to ctrl+ Alt + del, only
holding the power button down for ten seconds to reboot it brought it back.
Manually taking control of virtual memory and upping the amount, seemed to
fix it, it did, but not for long - so nothing else for it but to open it
up....

Nothing was socketed, apart from cables to accessories like the keyboard,
mouse pad, a USB + memory slot and wifi module. No socketed chips at all, 8Gb
of ram, none socketed and no expansion slots.

I managed to break the socket clamp catch for the tape type ribbon cable for
the USB + memory socket, trying to work out how to release it - It was a
matter of easing the keyboard a little way, to begin reaching in to unplug
things, some had a catch clamp which pushed in, others like this had a clamp
which needed lifting 90 deg to release.

I dusted the entire PCB, case and air ducts out thoughroughly with a paint
brush, then reassembled it, with no expectation that the lockup was fixed.
The damaged socket I partially botched by using a bit of sweetie wrapper to
wedge it and apply contact pressure.

No more lockups in the several days since then, despite changing it back to
W10 default virtual memory management - that USB + memory socket has power,
but no data, so obviously the cable has pulled partially out/ not making full
contact, in my rush to get it back together.

My best guess as to the problem - maybe a bit of loose solder or conductive
dust shorter something out. The brushing cleared it out.

Three main reasons why a computer runs slow and/or locks up - viruses,
hard drive on way out, heat.

I'll guarantee that the fan and airway was at least partially blocked
up causing heat buildup, so your brushing and cleaning sorted it