I’ll be honest: I have no answer for your question.
There are many possibilities, the most likely being there is not enough disk space allocated for restore points. In my experience, increasing that may or may not resolve the issue.
System Restore is so difficult to diagnose, and I hear of so many problems and misunderstandings with it, that I now avoid it completely. I turn it off completely. It’s not worth it to me.
I’ll tell you what I do instead.
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What System Restore is
In reality, it backs up more than the registry, but exactly what else is complicated, and more importantly, incomplete.
As a registry backup, it’s reasonable. When it works, it’s a fine way to take a snapshot of the registry that you can restore later, should something go wrong.
But only the registry.
What System Restore is not
Ironically, “System Restore” does not restore your system.
More specifically, it does not restore everything to the state it was at the time the restore point was created. It restores some things — like the registry — but not all things – like your files or whatever else you were hoping it would.
System Restore is not a substitute for backing up your system.
System Restore in the wild
Much of my opinion on System Restore is not based on its definition, or even its intent.
In theory, it’s a great concept, though poorly named, as System Restore doesn’t restore your system. I’m not a fan of its user interface, but that seems to be improving, and doesn’t really factor much into my opinion.
What does factor into my opinion is that in the real world, System Restore continues to have problems.
Your inability to manually create a restore point is just one example among many. Other common examples I hear include failures when restoring and missing or non-existent restore points.
Yes, sometimes, these are configuration issues. Sometimes, these are issues of mismatched expectations.
But often — too often — even understanding what should and should not be appropriate to expect, System Restore just lets people down.
System Restore successes
To be completely fair, I do hear of successes. It’s not uncommon to hear of problems caused by installing some application or another to be completely repaired by reverting to a recent restore point.
Like I said, it’s a great concept.
But in my experience, you just can’t count on it being there when you need it.
Don’t rely on System Restore
Given that it might work, but might not, what should you do?
Simple: don’t rely on System Restore.
Leave it enabled, if you like, but don’t count on it being there when you need it. Don’t set things up such that a System Restore failure would cause you grief.
Be happy when it works; be prepared when it doesn’t.
Instead of System Restore
What I generally advise is to turn off System Restore completely (to free up the disk space allocated to it), and rely instead on a good system backup strategy.
By “good backup strategy,” I mean that you regularly take full system backups of your machine, augmented with more frequent incremental backups — typically, monthly full and daily incremental.
If something goes wrong, restore from the most recent backup. Done. Everything — everything — will be restored to the state is was in when the backup was taken.
Yes, this can take more time than restoring to a System Restore restore point. Restoring from an image backup restores your entire system. But it’s worth it, because it works.
It’s what I do.
Choosing to leave System Restore enabled is a fine approach, but only in addition to having those backups. That way, when System Restore works for you, it’s a shortcut — a time saver.
And when it fails, it’s not a disaster.