There are occasions when, for one reason or another, clicking the Activate windows Option on the main start menu does not work. Either nothing happens or you get so far through the procedure and then the whole thing freezes. Here are two alternative options
1/ Click the Start button.
2/ From the Start Menu click Run.
3/ In the Run dialog box type 'oobe/msoobe /a' (without the quotes) Next click OK.
4/ Once the 'oobe' (Out of box experience) starts simply follow the on screen prompt.
1/ Reboot your PC.
2/ As your PC boots keep tapping the F8 button.
3/ When the onscreen menu appears select the Safe Mode option.
4/ In Safe Mode click the Start button.
5/ From the Start menu click Run.
6/ In the Run dialog box type: 'regsvr32.exe regwizc.dll' (without the quotes) and then click OK.
7/ Next type: 'regsvr32.exe licdll.dll' (without the quotes) and then click OK.
8/ Finally Reboot your machine to the normal Windows XP desktop.