SSD Controller Failure
An SSD that suddenly stops being detected shares its symptoms with a dead hard drive, but nothing else about it does — there's no spinning platter or moving head involved, and the actual recovery problem is almost entirely different.
What's actually happening
An SSD has no fixed mapping between the "logical" location the operating system asks for and the physical flash cell that data actually lives in. A controller chip maintains that mapping dynamically — usually called the flash translation layer — and spreads writes out across cells through wear leveling, so no single cell wears out faster than the rest. If the controller itself fails, corrupts its own firmware, or loses access to the tables it depends on, the drive can stop responding entirely even though every flash chip on the board is untouched and still holding data.
How recoverable this really is
How well this goes depends heavily on the specific drive model and manufacturer. Unlike hard drives, where recovery techniques are broadly similar across brands, SSD recovery generally requires understanding that particular controller's proprietary translation scheme — sometimes with encryption layered on top — just to correctly reassemble data straight from the flash chips. Some controller and vendor combinations are well understood by specialized labs; others, especially newer or less common models, may have no practical recovery path at all. SSD controller failure ends up covering a wider range of outcomes than most other scenarios in this catalog — everything from fully recoverable to not recoverable by anyone at all, depending almost entirely on which controller is involved.
The general approach
Diagnosis usually starts with identifying the exact controller chip and firmware revision, since that determines which approach, if any, applies — ranging from firmware-level repair to, in more involved cases, desoldering the flash chips and reading them directly, then reconstructing the data using knowledge of that controller's specific translation and wear-leveling algorithm.
Don't repeatedly power-cycle a non-detected SSD hoping it wakes up, and don't attempt any DIY firmware or chip-level fixes found online. SSD firmware and controller repair is far less standardized than hard drive work, and a wrong move at that level is rarely reversible.
Practical, step-by-step guides for specific recovery software will be added here as separate linked articles.
This page describes the general situation, not a guaranteed fix for your specific case. If you'd rather have someone experienced take a look before you try anything, see what a hands-on evaluation looks like.