Installer

I am running Windows XP Home Edition on my computer. After I installed the operating system, it works properly and without problems. Every now and then, sometimes after 2 weeks, sometimes after 3 months, my Windows XP Installer gets damaged. Unfortunatly I can't make out the reason. I already tried to set the system back to a system restore point but it didn't work. By meaning the Windows XP Installer gets damaged i mean, if I try to install programs with the Windows-Installers the message: "Windows Installer service could not be accessed. Contact your support personnel to verify that it is properly registered and enabled" occurs. This occurs for each programm i try to install, which are using the Windows Installer, every other program with own install routine works fine. Unfortunatly a restart of the computer as well as redownloading the installer file does not work. I would be glad to get a working Windows Installer or an other way to install programs using the Windows Installer without reinstalling my operating system every time.