Windows Vista problem

[delboy]

Hi,yesterday I started up my PC as normal (administrators account) and was met by the default vista desktop.All my documents,pictures,videos,contacts and music gone.All settings were back as they were when I first turned the PC on.All my programs were still there but all but 2 had to be re configured(ie prompted to register as if it was first time prog was being used).Luckily I had 95% of my data backed up and I have had to transfer all my files back.I set up a standard account which runs perfectly apart from my accounting software doesn't seem to exist.The admin account however doesn't always load properly(back to default settings although all my data is there).When it does seem to load correctly I can't use Windows media centre,it just stops working,I click on connect to my isp and am told there is no isp(but everything is fine on my standard account.Does anyone know what has happened and how I can cure this?