Use the Restoration Disk.
When asked choose Repair. Non-Destructive Installation.

Don't have the disk?
Example from USA;

The disk is free. The shipping and handling is not.
$17 for a 5 to 7 day ship, $24 for a 2 to 3 day ship.
Call 800-474-6836, 24 hours a day, 7 days a week.

Have the Serial Number written down, to give to the nice representative. This is in the white Service Tag, on the Bottom of the laptop. S/N = Serial Number.

[NOTE*
Do NOT post the serial number on a world wide public forum.
ONLY give to an authorized HP representative ]

For all countries use HP Support Worldwide, for the contact phone number,

http://welcome.hp.com/country/w1/en/support.html

The Restoration Disk will just repair the basic Windows files.
Boot Manager is one of them.

Regards,
joecoolvette