Thanks for the post. PCG-71312L is hardware configuration code given by Sony as manufacturing # for the computer. Try to locate the model # starting with SV/VPC/VGN continued with alphabets and then with numerical values. You can locate the model # on a small label on the bezel of the LCD display or on the LCD hinge or at the top left or top right of the keyboard.
Check if the hard drive is listed in the BIOS. Restart the computer, press "F2" key when the VAIO logo appears to log into the BIOS (For Windows 8, press the ASSIST button then the F2 key).
If the hard drive is not listed, the issue may be related with the hardware. Reset the BIOS once. Use the arrow keys on the keyboard to locate the "Exit" button and select "Load optimized or default values" option on the BIOS Screen. Then, save the settings and exit the BIOS setup.
If the hard drive is listed, follow the steps from the following link: