Spent the day buried deep within the registry of elderly friend`s Win-Vista laptop............the sudden demotion of their user privileges, the appearance of a Windows single-user password requirement (to which the required password was totally unknown) and the resultant absence of any administrator-level access, meant they were locked out of the crippled notebook which then seemed utterly useless.
I managed to get access to a CMD line using a bootable Linux utility and after lots of research found what and where to edit and have got things sorted.
Several malicious items which were likely to have been implicated, came to light during a deep-cleansing sweep; all now remediated.........over 6 hours of headscratching work in total, but I like a challenge and now I`m feeling satisfied with the outcome.