At first glance, this question seems simple enough and a quick answer would be that a hard drive is not worth repairing. However, in order to answer the question properly, we must first make a few distinctions and clarifications. There are certain circumstances in which a failed drive can be repaired.
There are two basic types of hard drive failures: logical and physical. Logical failures occur when system files are corrupted or accidentally deleted. They also occur from improper shutdown procedures or power failures. Because the drive is not physically damaged, a good data recovery software program like Data Rescue 3 can often be used to recover all the data from the drive.
Physical drive failure is quite different. Imminent physical failures are often signaled by grinding, clicking or other noised emanating from the drive. The causes of physical failure are varied: normal wear and tear, power surges, natural disasters and physical abuse. While a physically failed drive can be repaired, it is usually not cost effective or feasible. New drives have become so inexpensive that it makes better sense to replace the drive instead.
Nevertheless, you may need the assistance of a data recovery service to retrieve your data from the hard drive if you do not have the data backed up on a separate drive. RAID hard drive data recovery is especially tricky because of the various configurations possible. Internal and external hard drive recovery is simpler, but still requires the expertise of a recovery service to ensure success.