I am guessing you upgraded from XP to Vista, is that what you did? Were there any errors or complications during the upgrade process?
I am not certain but the reason the restore point might be missing is because it was deleted during the upgrade process. If XP and System Restore related files are not intact, naturally restore functionality would be lost.
May be somehow who has hands on experience could chime in since my educated guesses may not be accurate.
If possible, provide more details on what you did exactly and the answers to the questions I asked above.

~TL