how do i install an opperating system on the hard disk?

[baboski]

product name hp pavillion product number a6z59ua

[techgrl38]

Hello and thanks for joining the HP forums.  If you have replaced a hard drive on your notebook you will need to order recovery discs in order to reinstall the operating system.  You can order recovery discs here:

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00810334&cc=us&dlc=en&lc=en.  Thanks.

[3baller]

Is this a new Hard Drive?  If not then you can try going into the recovery manager if it still exist by pressing F11 at boot up.  From here you can run a recovery that will take your system back to factory defaults wipping all data off the drive.  You could also order recovery discs from HP if you need the OS. Hopefully this helps.