Could you list a series of steps coming from your experience that one can use to check if an internal laptop HD (let say, SATA drive) is definitely broken?
Step 1 - Verify that the BIOS can see the drive. Reboot and enter your BIOS's menu and verify that the drive shows up there and has correct specs.
Step 2 - Rule out the OS. Boot from a CD/USB and verify that the drive is present and readable.
Step 3 - Rule out the other hardware. Try the drive in another machine/enclosure.
Step 4 - Run diagnostics. Many drive manufactures provide drive diagnostics on their web sites. Many also require you to have a failing test before sending the drive in for warranty replacement. These tests are useful even for out of warranty drives. If the manufacturer doesn't provide test utilities, there are open source "rescue" CDs that can run more generic tests.
You may wish to swap #2 and #3 depending on how easy it is to perform one or the other.
Step X (last resort) Put the drive in the freezer for a few hours.