If it is the only computer, then all you’ll need to do is to ensure nobody open any suspicious emails. (emails from unknown persons and attachments, no matter the header and contents).
If networked, then some steps should be taken, such as the disabling of the server and workstation services if you don’t access other services via the network (such as file and print sharing).
Also, if you have any backups, just zip/tar/arj it all up into one big file, and append .wcry to the filename, eg mybackup.arj.wcry
I’m not 100% sure, but it should do the trick and stop it from getting encrypted.
FWIW M$ should have made the free win10 upgrade available for XP and upwards.
Had some good memories with Vista (no crashes, it was solid and reliable surprisingly), but Win7 outperformed it.