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OSX is very secure and unlikely to be hacked unless you have some evidence to suggest otherwise?
Have you monitored the main system processes?
You can ignore any automated offers sent by this website offering remote assistance.
It is very unlikely that you have been hacked - the encryption that Apple uses is extremely secure, even the FBI cannot hack it.
Since you are unable to boot up the Macbook this suggests a hardware fault, possibly a fan has failed and caused it to overheat and go into protect mode. If you are unable to carry out any hardware checks and repairs yourself, you will need to take it to an Apple store.