Hi:
Depending on the age of the notebook, with the disk 1 of the recovery set in the dvd drive, restart the PC and at the beginning of the HP welcome screen, either tap the ESC key (menu of options) or the F9 key to get the one time boot option list.
Select the boot menu if the ESC key gave you a list of options and select the DVD drive from the list of boot options and the same for the F9 key.
Watch the screen for instructions.