My Macbook Pro 2013 13inch has gone from being the fastest computer I own to the slowest overnight and I'm wondering if the Samsung Evo SSD inside it is failing. Every click or scroll is followed by a beachball and the machine freezing for around a minute, trying to do anything on the machine takes about 5 times as long as usual. On boot up I keep getting the prohibitory sign which suggests the machine can't find the SSD to boot, however this only stays on for 15 seconds and then the machine proceeds to boot into Sierra. Last night I tried to do an erase and reinstall. The erase went fine but the reinstall didn't move an inch and I left it overnight. I'm going to put an old formatted hdd in to see if I can install the OS and boot from that, but just curious to see people's thoughts on this??