OS disappears on HDD

[Avents]

Hi everyone,

My hard drive recently crashed so I decided to buy a new one. Ibought a hybridd HDD/SSD and plugged it into my Macbook pro (mid 2013). I created a bootable USB to install Yosemite, partitioned the HDD, and started the Yosemite install.
Everything went well, I could boot up to the desktop, connect to the internet etc.
I then turned off my computer, and when I turned it back on, I saw the blinking folder with a question mark. I tried reformatting my HDD and installing another OS X, which worked, but once I turned my computer off, I got the same blinking folder problem at startup.
I get the impression that everytime I shut down, the HDD is being "reset", and all the information gets wiped.

Does anybody know how I should proceed ? Is the HDD or the mac the problem?

 

[Fishrrman]

Have you opened the startup disk preference pane, and designated your new internal drive (and the OS on it) to be your startup disk?

 

[Avents]

Unfortunately not :/
Is there a way to do this now that I can't access the desktop ?

Also, even when I press option, the drive doesn't pop up, so do you still think it's because I didn't set it as the startup drive ?

 

[Fishrrman]

Try this:

- Shut down, all the way off
- Press the power on button
- As soon as you hear the startup sound, hold down the option key and KEEP HOLDING IT DOWN.
- Does the startup manager appear?
- Do you see your "main drive" (the one you installed the OS onto) in it?

If so, use the pointer to select it, then hit return.
What happens now?