Turning system restore back on I believe creates a restore point at that time.
Or you can do it manually:
1. Click Start, All Programs, Accessories, System tools, System Restore.
2. In the pop-up that appears fill in the radio button to Create a Restore Point
3. Click NEXT
4. Enter a useful name that you will remember if you need to find this again (Clean Restore Point)
5. Click CREATE