There are a few reasons that the VS Recorder won't recognize that a hard drive is installed or a "Drive Not Found" message appears:
there's either not a hard drive installed, the hard drive has lost connection somehow or there's a malfunction.
The VS-1680 will need to be opened up to determine if a hard drive is installed or not; and if one is installed, the drive may either need to be reconnected, replaced or the VS-1680 will need to be serviced.
Note that because of safety and liability reasons, we cannot offer instructions regarding how to open up a product. We recommend having a qualified service technician do this. The following page has information regarding service:
https://www.roland.com/us/support/service_repair/
The following article has information regarding hard drive compatibility:
https://www.roland.com/us/support/knowledge_base/201975829/
Kind regards,
Roland Product Support