That sounds almost certainly like impending HD failure.
However, to completely exclude the possibility that it's a problem with the SATA/IDE-to-USB adapter, you could try to connect this SATA harddrive internally by opening up your PC and plugging it directly into one of the motherboard's SATA ports and connecting power to it. (Obviously, don't do this with the PC turned on.)
If you're then able to read the drive OK, it's the USB adapter. If it fails again, I hope you can afford a new harddisk.