System Restore's job is to keep notes of everything you change on your computer, enabling you to reverse them with a couple of clicks.
On Windows 7, right-click Computer, select Properties > System Protection > System Restore > Next, and choose the restore point you'd like to use. Click the new button to 'Scan for affected programs' and Windows will tell you which (if any) programs and drivers will be deleted or recovered by selecting this restore point.
Mentor Graphics applications can sometimes be adversely affected by other programs that are installed and registry settings that get changed. Reversing those changes by returning to a restore point can get Mentor software back up and running.