Desktop PC had two SSDs and one standard hard drive, which held data. PC failed and would not reboot until I removed the standard hard drive, so I presumed hard drive failure. Replaced it with another SSD, Intel 540S. It installed fine, but then it disappeared several hours later. I changed out the SATA cord and then the power cord. When neither worked, I changed the drive designations, but that step did not work either. It still appears, works fine, but then hours later goes away. If I unplug the power to the SSD, plug it back in, and then reboot, it is recognized again for a few hours. I am at a complete loss as to what could possibly be causing the problem. Any ideas?