User.dat file troubles using Teatimer

I am using ‘Teatimer’ as it is part of the ‘Spybot’. It is asking me to change the registry settings. I would like to secure my computer from some users. I am also planning to change the OS to Windows 98 Standard Edition. I have deleted the password of AOL dialup connection and deleted the password of Hotmail login from Mozilla Firefox and Microsoft IE. The ‘Teatimer’ asked to save the changes accidentally I selected ‘NO’. After the rebooting of the computer it gives me an error message which says that ‘the application has performed an illegal action and it is going to quit. Please contact the vendor.’ The error message comes with a title ‘Explorer’. When I click on the error details, a paragraph of details comes and if you need I can provide the same. I have tried by booting the system in safe mode. But there is no icon in the desktop and it shows the same error message. Is this the problem with the user.dat file? Please help me to get out from this problem, so I can avoid the re-installation of Operating System. I will be thankful in advance for all the help and support.
