If you are getting rid of an old PC or laptop, you should either remove the hard drive or destroy it to protect your data. People have been known to scavenge hard drives from tips and retrieve sensitive personal, medical and financial information.
Selling dead machines for spares or repair is even riskier, and how much would your Laptop be worth? I doubt it will fetch enough to make it worth spending the time and (probably) money needed to erase your data. And, of course, if you don’t do it, you could be at significant financial risk, depending on the information stored on it.
Whether or not the buyer replaces the motherboard, they will probably be able to read your hard drive, unless you encrypted it with an unhackable password. This is unlikely.
Because your laptop won’t boot, you will have to do what an attacker or repairer would do: remove the hard drive from the laptop. However, if you want to delete your data and reinstall the hard drive, you will need either another PC or a hard disk eraser.
If you have a desktop tower with a spare drive bay, you can mount the laptop drive inside, by connecting the power and data cables. This is easy and if you have another laptop, you can mount it in an external hard drive enclosure, then connect it to another PC via a USB port.
In theory, you could also use a degaussing machine, which uses very strong magnetic fields to erase all forms of magnetic media – disks and tapes. We provide this service and you can read more HERE.
You could, of course, simply destroy the hard drive physically, which is what some government departments prefer. Read about how we can safely and securely destroy your Hard Drive.
It’s easy to delete the data on a hard drive in a working PC or in an external USB enclosure. It’s not quite so easy to erase it completely. When you delete files, the operating system doesn’t erase them, it just removes them from its directory. This frees up the sectors for use by other programs, so most of them will be reused eventually. Until that happens, someone with an un-erase program can locate the data sectors on the hard drive and reconstruct the original file.