When you install any software, if the installation is not proper or because of some other reasons sometimes, Window refuses to boot after restart. Windows can be booted in safe mode in such circumstances, but the installer will not work. When yo reboot in safe mode, you need to create a registry entry for Windows installer to work for install.
NB: If you use the registry editor incorrectly, you might cause serious problems that might require you to reinstall your operating system. Use the registry editor at your own risk. Keep a backup of registry before editing.
To create a Registry entry, open command prompt ( Run->Cmd). Type the following command in the Window- REG ADD HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\MSIServer/VE/TREG_SZ/F/D %Service%
You can also create a entry from registry editor.
Next start the Windows Installer Service by typing net start msiserver. Once this is done, you will be able to install/uninstall applications in safe mode.