Firstly, thank you all for your help, which is why unfortunately I am here again tonight as my work colleagues keep bringing me thier ailing pcs's.
This laptop running windows xp media centre has somehow had the welcome screen deactivated by one of my colleages kids so that it logs on with only 1 user and the other user accounts are not available.
They are still listed in the user acounts in control panel, but when I try to change the way that users log on both the welcome screen and fast switching options are greyed out and I get the error message that "client services for windows has disabled the welcome screen and fast user switching.To restore these features you must install client services for NetWare"
I don't know how it happened either.
I've researched some previous threads and downloaded a program called xp_fixlogon, but tit appears as if the default gina is in use?