|which specific component is bad is hard to determine. what i can say with a certain degree of confidence is that it's probably time to get a whole new computer.|
"check the cables and power drive"
could be that the HDD just can't spin as fast as it used to, and it's just your HDD that's bad. but this could also mean that your power supply unit (PSU) can't get the HDD the juice it needs to operate correctly. A faulty or dying PSU will slowly cause damage to ALL of your other components (motherboard, CPU, video card, RAM), and if you've been having stability issues for a while, it probably already has. it could be a dying motherboard or bad RAM, causing data corruption that cause your HDD to fail tests. The "it could be" list is quite long.
i know buying a new PC to fix the issue is like shooting a fly with a bazooka, but consider the alternative: you spend money on a new HDD, and a bad PSU, RAM, motherboard, etc causes damage to your new HDD over time until 6 months from now you're having the same issue. The same scenario would hold true if you only replaced the PSU, motherboard, cpu, etc., so the safest thing to do is upgrade everything. in other words, get a new PC. 6 years is ancient by PC standards.
hopefully, you've already backed up the data on this HDD?