Answer:
a. SATA cable
Explanation:
A troubleshooting process could be as follows:
Then, two alternatives remain:
In the reliability configuration of the components, the hard drive depends on the SATA cable to work properly. A faulty SATA cable would prevent the hard drive to work correctly. Then, a loosely SATA cable is the first thing to check before proceeding with the hard disk.
Additionally, a loosely SATA cable is also a common source of error messages like "OS not found" and it would be easier step to be discarded before continuing with a more demanding one like checking the hard drive.