how do you restore factory default settings or reset completely windows vista hp pavilion dv9927 cl notebook pc

Power on the PC and hold F11 (on some models you may have to press ESC + F11). This will, provided your recovery partition is still intact, boot the PC into recovery mode where you can select to restore the PC to factory defaults.

If the recovery partition isn't intact anymore or doesn't work, you will have to boot the PC from the recovery DVD's you made when you firs got the PC.

Recovery from Windows Vista desktop:

From the Windows desktop click Start  , and then type recovery manager in the Search field.
Select Recovery Manager from the list, and then press the Enter key. Allow the action to continue if prompted.
On the Welcome to the Recovery Manager screen, click Next.
On the Software Program Re-installation screen, select No, and then click Next.
On the Hardware Driver Re-installation screen, select No, and then click Next.
On the Microsoft System Restore screen, select No, and then click Next.
On the Recover your computer to its original factory condition screen, click Yes, and then click Next.
On the Welcome to the Recovery Manager screen, click Next.
On the Microsoft System Restore screen, select No, and then click Next.
On the System Recovery screen, confirm that you want to run a System Recovery by selecting Yes, and then click Next.
The Recovery Manager gives you the option of backing up your data files. To do so, read Backing up your files.
If you do not want to backup your files, select No, and then click Next.
After the System Recovery is complete, the computer restarts and continues into Windows setup. Complete the setup screens and wait until the computer finishes the setup. Then, turn off the computer, reconnect all peripheral devices, and turn on the computer.
Before using the computer, update and protect your computer. Reinstall any virus and security software that was installed before the System Recovery.
Reinstall any software applications that were added after purchasing the computer, and any files that were backed up.



Run Recovery partition on the hard disk drive from powered off:

Turn on the computer and immediately press the F11 key repeatedly, about once every second, until Recovery Manager opens.
On the Welcome to Recovery Manager screen, click Next.
On the Microsoft System Restore screen, select No, and then click Next.
On the System Recovery screen, select Yes, and then click Next to continue the recovery process.
The Recovery Manager gives you the option of backing up your data files. To do so, read Backing up your files.
To continue recovery, select No, and then click Next.
A recovery progress screen opens. Wait while files are restored.
When System Recovery is complete, click Finish.
The computer restarts and continues into Windows setup. Complete the setup screens and wait until the computer finishes the setup. Then, turn off the computer, reconnect all peripheral devices, and turn on the computer.
Before using the computer, update and protect it by reinstalling any virus and security software that was installed before the System Recovery.
Reinstall any software applications that were added after purchasing the computer, and replace any files that were backed up.


NOTE:
If the RECOVERY or FACTORY_IMAGE partitions on the hard drive have been deleted OR the files in these partitions have been deleted, these steps will not work. You must use recovery discs.


Reference:
http://support.hp.com/us-en/document/c00809678