I only know of this issue as I've had it once previously and it turned out that Adaware's updater program somehow corrupted the XP userinit.exe & or winlogon.exe file but my memory of the incident is a little vague
I called to their home to look at the PC and when I saw the logon issue I asked if Adaware is installed and they confirmed it so here we are. Does anyone have a quick solution or link to an old thread (maybe mine, LOL) from the archives maybe? searching hasn't thrown up much, sorry
I'm going to poke around the HDD now via a HDD reader to see if I can access & replace files to get it up & running.
TIA
Andy
ps: it's running media centre edition so formatting it is not an option.