I installed a new hard drive in my 2009 Macbook Pro 15. The previous one moved to an external enclosure. I do not own any installation discs for this laptop, yet I somehow need to get an operating system loaded. When I turn on the machine, it displays a white screen with a light-grey folder bearing a question mark, flashing. I have tried holding down keys to enter Disk Utility or Safe Mode, to no avail. Holding ‘option’ does remove the folder icon, and produce a cursor for the trackpad, yet no more than that. How do I get an OS on this hard drive?