Last week my mbp has a folder with question mark blinking and it does not boot. I have 256gb Samsung 830 SSD. I visited Genious bar and they told me that SSD could not be found. The. I switched back to the original HDD and it works. I decided to send the 830 SSD to Samsung for replacement. However they told me that the SSD passes all the performance tests. I got the SSD back today and installed it in my MBP, however the SSD does not show up in disk utility. Called Samsung and they told me to try secure erase by using Samsung Magician. But I don't have access to a PC, what can I do now? Thanks.