All was well in the end - he slept for an hour after lunch !
That's good. I do not know what system you have but I have Windows 7 and I have listed the sequence for changing the way that updates are installed on mine:-
Select Start (bottom left corner)
Control Panel
System and Security
Windows Update
Change settings (top left of screen)
The heading at the top of the page now reads “Choose how Windows installs updates”
Under “Important updates” click on the arrow in the box underneath and from the options select – “Check for updates but let me choose whether to download and install them.”
Under “Recommended updates” – tick the box for “give me recommended updates the same way I receive important updates.”
(There are other boxes you can choose to tick for various other options)
Click on OK at the bottom of the page.
I have my computer set this way. If there are updates you can install them when you want so it doesn't slow the system when you are busy. When I log in, if there are updates my computer flashes up a message in the bottom right corner saying updates are available to install. If it says that it needs to shutdown after installing the updates you can also select to postpone this if you are busy.
If your computer is slow you may need to do a disk cleanup. There are several ways to do this and how you do it depends on the system. Post again if you need help.