Click Start followed by Run …

… type msconfig in the Open box, and then click OK.
On the General tab, select Normal Startup – load all device drivers and services.

Click OK …

… and then Restart to restart your PC.
Click OK when the message warning you that you have used the System Configuration Utility to change the way in which Windows starts is displayed.

Relevant Microsoft Knowledge Base Articles
- 310353: How to perform a clean boot in Windows XP
- 310598: Overview of the Windows Installer Technology
- 555175: How to resolve Common Windows Installer Problems
- 292539: How to obtain the Windows Installer engine