I used the CS3 trial cleaner to allow me to enter a serial number when a system restore prevented CS3 from loading. Before I cleaned and reinstalled CS3 I tried to undo the last restore and a restore to a date after cs3 was installed but not activated. I could not start CS3 until I ran the cleaner. It may not be intended for this use but it was the only thing that worked. It did not allow a trial period but did allow me to enter the serial number and activate. I did not have to format or reinstall any other software.