The PC at home, a 2012 Dell Vostro i3, has on occasions decided to suffer from a 'hard disc failure, press F1 to continue' message. A switch off and on again fixes it (well it is Windows afterall) but it then takes about 10 minutes to finish restarting before it operates without delays.
That sounds a lot like what happens when the disk bearing gets a bit sticky, and it takes longer/several attempts to spin up. The disk isn't ready by the time the BIOS looks for something to boot from, but once warmed up and spinning it works.
This failure mode gets progressively worse. If the disk dies completely, you may be able to encourage it for long enough to get the data off with the freezer treatment or a little percussive maintenance, but hopefully it wont' come to that.
a: I was wondering if it is worth swapping the disc with a SSD of the same size to improve startup and avoid a total drive failure. Could I just do a disc copy, is it image (??) to a new drive?
Certainly. I'll defer to the Windows experts for how to go about doing it, as my go-to-approach of Linux and dd is likely to be over-complicated...
b: would increasing the RAM from 4GB to 8GB make much of a diference if an SSD is fitted?
Depends on whether the machine is low on RAM in normal use (it might not be if you're just running a web browser, say). It certainly won't hurt (I wouldn't want a desktop with less than 8GB these days
[1]), but you'll likely see more immediate benefit from the switch to SSD.
[1] I'm currently using 2.7GB of RAM with another 1.8GB allocated as buffers, but this is a relatively lean Linux desktop running a browser, mail client and an assortment of terminal windows running ssh to elsewhere. I occasionally do things with large files that justify having 16GB, though.