Most likely a serious hardware error/failure.
Could be the Hard Drive or one of several other components. The only quick way to determine it is by substitution. If you do not have a range of spare parts, it's best to take it to the experts.
Could be the Hard Drive or one of several other components. The only quick way to determine it is by substitution. If you do not have a range of spare parts, it's best to take it to the experts.