After boot however, my whole desktop was replaced by a saying to "click here and install our security software.. (or something) ". I didnt. Task manager and Windows Update also didnt work. After much fiddling (by then it was,like, midnight) i managed to find out i had a whancer adware and uninstalled it, by the simple mean of using the control panel: at that point, i reenabled task manager from the admin console and could also restore the wallpaper.
Windows update still doesnt work tho: automatic updates seems to be enabled from the control panel, but not in the security console screen - i also get a tray popup from it; the service used for manual updating is also disabled and won't start (doesnt even tell the reason).
At this time i'm at work, so i cant readily provide more information or try solutions for the next four hours - if anyone could provide me with the right advice, however, i'd be thankful to him for life.
PS - excuse me for not using standard terms in relation to components and services, but i have the italian version of Windows XP