It really depends on the kind of failure that you’re experiencing.
I want to be clear about one thing when it comes to registry backups: they are not a complete backup solution. Even if what’s preventing you from booting is a registry issue, the only real, true backup solution to the scenario that you described is a full image or machine backup. A registry backup simply cannot save you from every possible failure mode – even those that involve the registry itself.
Which may leave you wondering, “If I can’t restore a registry backup, then what good is it?”
It’s simple, really: most failures aren’t that catastrophic. Not all failures prevent you from rebooting and restoring the registry.
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How to restore your registry
I don’t know how your machine is failing to reboot – meaning I don’t know exactly what symptoms you’re seeing – but see if you can boot your machine in Safe Mode. During the early boot process, right after the BIOS self test, press F8 to get the boot choice menu and select the option to boot into Safe Mode.
Safe Mode can often sidestep some of the issues that prevent a full boot from working and it’s perfect for restoring the registry. In fact, that’s what most computer repair professional will choose when doing a full registry restore.
I have to stress that it’s not guaranteed, but it’s the best approach for where you are.
Why full backups are important
In reality, backing up the registry is more about protecting yourself from other, less serious types of failure: applications that won’t load, settings that get lost, and applications that start behaving “funny” after you’ve made some kind of change to the registry.
In those cases, you can restore the registry because you are able to boot, you are in Windows and you have the tools and resources to do so.
But for a full, catastrophic failure where the registry itself – or for that matter just about anything – prevents you from rebooting into Windows, a backup of the registry is simply not enough.
You may need a full system backup that you can then restore to get your machine working once again.