Agree with Dennis - if it wasn't trashed after being dropped, it is now that you've opened it 
The tiniest speck of dust is many times the size of the gap between the heads and the platters which is in the order of a few nano-metres. The head floats on an "air bearing" - a tiny cushion of air.
The diameter of a human hair is many times the size of the flight gap - the smallest speck of dust is massive in comparison (in the order of 1000s of times larger - it might as well be a brick).
Modern drives (SATAII / SATAIII etc.) have an interface called SMART(Self-Monitoring, Analysis and Reporting Technology) which, assuming the drive is at least responding electrically, allows a technician to interrogate a drive as to its health and to control lots of parameters. Many drives have accelerometers in them and they record any impact that the drive has incurred, so when it goes back under warranty, the manufacturer can see what's happened to it. You can also interrogate the SMART interface yourself with tools like GSmartControl.
HTH
The tiniest speck of dust is many times the size of the gap between the heads and the platters which is in the order of a few nano-metres. The head floats on an "air bearing" - a tiny cushion of air.
The diameter of a human hair is many times the size of the flight gap - the smallest speck of dust is massive in comparison (in the order of 1000s of times larger - it might as well be a brick).
Modern drives (SATAII / SATAIII etc.) have an interface called SMART(Self-Monitoring, Analysis and Reporting Technology) which, assuming the drive is at least responding electrically, allows a technician to interrogate a drive as to its health and to control lots of parameters. Many drives have accelerometers in them and they record any impact that the drive has incurred, so when it goes back under warranty, the manufacturer can see what's happened to it. You can also interrogate the SMART interface yourself with tools like GSmartControl.
HTH
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