Do what it takes, I'm afraid...
You definitively need to attach the SATA power lead. I made mention of it because for other users that SATA connection was difficult because it couldn't be reached or more effort in order to do so. If there is cable strain it may pull off or simply not be a full contact. if that's the case, buy a SATA extension lead or convert a Molex type to SATA type which in many cases are generally available(un-used) and longer.
Sorry, if this seems overall, hit and miss but USB 3.0 doesn't work for everyone because of all the various h/w combos, toxic or cheap h/w out there. Those that have issues complain but the fix maybe more than a simple cure, as such. The variables are just there and may not be overcomed until money is thrown at it. Which is why i mentioned to try another brand USB 3.0 card. Just make note of IC chip on-board that makes USB 3.0 possible.
good luck -----Willy