Folder with sign question (no issues in hardware) - help I got a macbook pro 13inchs (2011), Yosemite.
One week ago a folder with a sign question appeared in the first screen and that's where all my problems started.
I follow some links in order to reinstall the operating system but seemed like there wasn't disk on the macbook. 
I did two things:


I bought a new disk and I installed it.
Then I performed a diagnostic test in order to check if there was a hardware problem: no problems. 


However, I tried once more to reinstall the operating system but again seemed like there was no disk in the macbook.
I don't know what do from this point since the results from diagnostic test (exhaustive one) showed no hardware problem at all.
Pls, help me
The folder with a flashing ? is an indication that there is no operating system installed on your MacBook.  Depending on whether your MacBook is an early or late 2011, it may not be equipped to do internet recovery  by starting it with CMD-OPT-R.   If CMD-OPT-R does not begin internet recovery, then you need either a USB installer, a Snow Leopard DVD disk, or to take it to an Apple Store for them to install an operating system on your MacBook, which they'll usually do for free.