If the laptop doesn't keep the correct time, and date, it's because the CMOS Battery is shot.
In the HP Pavilion dv9000 series of Notebook PC's, the CMOS Battery is named RTC Battery. (Real Time Clock )
Replace the RTC Battery.http://h10025.www1.hp.com/ewfrf/wc/manualCategory?cc=us&dlc=en&lang=en&lc=en&product=1842189&
On the above page, scroll down, and left-click on the file name in blue -
HP Pavilion dv9000 Notebook PC - Maintenance and Service Guide
Ignore the following if you are aware;
This is a PDF file. The computer you are using now has Adobe Reader on it, which uses PDF files.
After you click on the file name it may take up to 30 seconds, before the first page comes up.
At the top of the PDF file is the page number box. It is to the Right of the Down Arrow.
You can use the Down Arrow to go page by page, until you arrive at the page you want, or you can do this;
1) Put your mouse cursor in the page number box.
2) Left-click once
3) Type the page number
4) Press the Enter key
Or you can use the Bookmarks menu to the left.
Go to Page 131.
5.7 RTC Battery
A) Remove ALL power. Remove the AC adapter (Charger) if plugged in, and remove the Battery. (Main battery)
B) I would advise buying an ESD wrist strap, and wearing it.
Connect it's alligator clip to a good ground source.
(Electro Static Discharge)
Average cost is around $3 to $6.
Your body carries Static electricity. Static WILL fry out (Short Circuit) the delicate hardware components inside a computer.
Use an ESD wrist strap, and breathe easier.
Don't know if you have ever replaced a CMOS Battery in a desktop computer before, but the Battery is the same.
It is just soldered to two wires, and put into a small plastic bag that has a cable coming from it, with a connector on the end.
(NO, I do not recommend trying to solder wires to a CR2032 battery! May go BOOM)http://www.vendio.com/stores/CMOSBATTERIES/item/hp-cmos-battery/replacement-cmos-rtc-battery-f/lid=3032230
The above is from a quick search. Scroll down for laptop compatibility
As you can see in the Service Manual, you need to remove;
1) The Memory Compartment Cover. Page 28
Table 1-8, Bottom Components
Number 6 points to the Memory Compartment Cover.
The RTC Battery is fixed to the laptop with double-sided tape.
New tape should come with the new RTC Battery.
If you have any additional questions please post in a Comment.