Ultra Fit USB 3.0 128 GB not detected

Have you tried putting it into a USB hub? I had mine die on me after 8 months and it would only be detected on a USB 2.0 hub. It would be best to return it, get your money back and buy another brand, like Corsair or Kingston. As most SanDisk drives heat up when in use and can actually burn you on some modles, like the UltraFit, and this is from experience.