You are mistaken on the hard drive.
Clean rooms are for disassembling the hard drive mechanism itself, but inside external hard drives like your USB enclosure is an interface card and the same kind of internal hard drive found inside desktop and laptop computers.
A first debugging step in a case like yours is to remove the drive from the external case and either insert it into a different one or plug it directly into a desktop computer if it contains the drive's native interface (this was usually IDE in past years but some newer enclosures use SATA drives within.)
If you're willing to expend a bit of energy, work, caution and $30, it's very likely that unless the hard drive mechanism itself failed, a kit like this one from Granite Digital would allow you to recover your drive's contents:
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