The solution is not foolproof. Even if someone is not able to boot your system he/she can easily get your data by using a live CD. So you might still want to keep your data encrypted.Prevent Your PC From Booting If Your USB Drive Is Not Inserted
Most of us are concerned about the security and privacy of our data. We put login passwords, encrypt data and do various other tricks to ensure that someone cannot access our system without our authorization. Hardware manufacturers have also started exploiting our desire for data security by offering fingerprint readers, face recognition and other fancy stuff. If you are paranoid about who accesses your system, you can use a simple trick to prevent the system from booting unless you want it to boot.