I'm having some trouble logging onto Windows XP. After click on user on welcome screen, it pops up a dialog box with nothing except yes or no to select. After selecting yes, it flashes the desktop for a few micro-seconds, then logoff again. If select no, it logoff straight away without flashing the desktop. I can login to safe mode, have done a virus scan and adware scan, could not find anything... please advice what can I do...