|If it is not in System Restore, you may have deleted it or you have decreased system restore disk space because one is created before SP1 or any other Windows update is installed. You may also uninstall SP1. But if you want to install SP2, then you actually need SP1(prerequisite). Otherwise, SP2 cannot be installed.|
By the way, when did you install SP1 ? SP2 is released about a year ago. SP1 ? I do not remember when.