Your computer will not reboot and you have tried several times. Microsoft Windows operating system will not boot properly? What exactly happens when it tries to boot up?
I would try using that computer's factory restore option if it has one. It might have a repair option. Also, you can try reseating that hard drive if it is a laptop computer.
You can try taking a hard drive out of that laptop and then inserting it again to see if it will boot. If the operating system will not even attempt to boot, then it is most likely a faling hard drive. You might be able to fix any bad sectors on it long enough to retrieve data off of it.
You would need a Microsoft Windows operating system compact disc or a hirens boot type compact disc to run a program that would fix any potential bad sectors. Hard drives tend to fail after a certain amount of time and or usage. Usually there are warning signs and symptoms, but this is not always the case.
Have you tried putting that external hard drive in a ziplock bag and freezing it for at least an hour? I have done it before and it works sometimes. It might allow Microsoft Windows operating system to run for around twenty minutes or so so that you can get data off of it.
It is not recommended to freeze your hard drive if you plan on taking it to a data recovery company as it can further damage that drive. These instructions and tips were written for Microsoft Windows operating system. However, you can use them for any operating system.