Can't erase SSD on main bay I have a MacBook Pro mid 2011.
I've installed a SSD on the main bay, removed the optical drive and installed a caddy with the a regular HDD on it.
The OS was installed on the SSD.
This setup works fine!

Last week I had to force a shut down by pressing and holding the power button. After that, my system didn't boot.
(a question mark apperars)

I install El Capitan again on my HDD and right now I'm trying to format/erase/restart my SSD.

If I change hard drives places (putting SSD in the caddy and HD on main bay) it works… I can erase the SSD, reformat, etc, using Disk Utility.

But with the HDD on caddy and the SSD on the main bay, my mac dont recognize my SDD and I can't erase, or format it.

My goal here is to reinstall El Capitan on SSD using it on the main bay because its faster and have a better performance.

Does anybody have an idea about it?
First, make sure it's not just a regular connectivity problem. I used to have an older MBP that displayed the same symptoms every now and then (with the stock HDD). Whenever it threw question-marks or missing file-system symbols at boot-time; I'd just pop it out, blow it like an old Nintendo cartridge, and pop it back in. If that's not the problem;




Make sure your AC adapter is plugged in and connected to your Mac.
Turn your Mac on, by hitting the power button, as per usual.
Press and hold:  ⌘ Command+R until you see the 
 Apple logo or the OS X Utilities.  
First off; you can try repairing and/or erasing your drive etc. via the Disk Utility.  
Finally; if all else fails, just select Reinstall OS X and follow the prompts.
The installer requires Internet Access. You can choose a network from the Wi-Fi Menu.
(top-right).