Where is the old drive? Put it into an external enclosure and startup from the Recovery HD. Then do the following:
Install or Reinstall Lion/Mountain Lion from Scratch
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Erase the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your new drive from the
left side list. Click on the Partition tab in the DU main window.
3. Set the number of partitions to one. Set the format type to Mac OS Extended
(Journaled.), click on the Security button and set the Zero Data option to one-pass. Click on
the Apply button and wait until the process has completed.
4. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
because it is three times faster than wireless.
No key takes you to Disk Utility. Disk utility is a program that run under OS X.
Depending on the age of your Mac you can use the Online Internet Recovery system, Hold down the Command + Option/Alt + r key at startup and if your Mac is new enough it will boot from the Apple servers from across the internet.
If your Mac is a little older and came with reinstall DVD discs then you would use the OS X disc to boot the system and run Disk Utility.