a virus scrambled my daughters laptop - after four days of repair installs, replacing software, firewalls antivirus etc etc etc etc, XP would not assign USB drive letters, I suspected that after Daemon tools had been damaged by the virus that somehow the drive letter assigning mechanism had become constipated but I didn't know how and searched the internet wilderness for another few days banging my head on various solutions - none of which worked (how do we rid the net of parrot syndrome) until I read royorlev's post. I downloaded SPTDinst-v142-x86.exe from
http://www.duplexsecure.com/en/downloads (note newer version now available royorlev's link now dead) and it fixed the problem. the exe ran fine in windows without safe mode or using command line. Anyway royorlev is my current hero - many thanks!