Final answer:
Loss of stored data and hard drive formatting is usually due to hard drive failure, malware, or system errors which can be caused by physical damage, software issues, or malicious attacks.
Step-by-step explanation:
If stored data and hard drive formatting is lost on a customer's computer, the likely cause is a hard drive failure, malware infection, or a severe system error. Hard drive failure can happen due to physical damage, wear and tear, or manufacturing defects. Malware can corrupt or encrypt data, making it inaccessible. System errors can occur due to software conflicts, incorrect updates, or accidental deletion of critical files