How do i change the cmos battery in my compaq presario 725US notebook?

Here is a video on youtube that shows how:

http://www.youtube.com/watch?v=R57XXxxLgoE

If the computer display remains blank and does not boot into Windows, or some device stops working, or the computer freezes, it may be helpful to perform a hard reset. A hard reset will erase all of the information in the computer's temporary memory and restore functionality. Many times, peripheral devices like USB drives, firewire devices, USB memory sticks, and even SD cards can interfere with the normal boot process. Doing a hard reset will force the system to clear and then reestablish the software connections between the BIOS and the hardware. Other problems that can be resolved by performing a hard reset include the keyboard not responding, or the PC not coming out of hibernation or sleep mode, or the PC freezing during normal operation. When performing a hard reset, you must disconnect or remove all devices. You should start and test the computer by itself, and then reconnect one peripheral device at a time. To resolve the start up or operational problem, you should run the HP Support Assistant, or manually install all updated drivers from Microsoft and HP. Performing a hard reset To perform a hard reset, follow the steps below.

1. Unplug the AC adapter from the notebook PC.
2. Remove the battery from the notebook battery compartment.
3. Remove the computer from any port replicator or docking station, disconnect cables to printers or devices such as external monitors, USB memory sticks or SD cards, headset or external speakers, mouse or auxiliary keyboard, turn off WIFI and Bluetooth wireless devices.
4. Press and hold down the power button for about 15 seconds to drain any residual electrical charge from the capacitors that protect the memory.
5. Insert the battery and plug the AC adapter back into the notebook PC; but do not connect any of the peripheral devices.
6. Press the power button to turn the notebook PC back on.
7. If prompted to boot into Safe Mode or select a special type of start up, use the arrow keys to highlight Start Windows Normally , and then press the enter key.

The battery is mounted on the mother board, it is about the size of a quarter. look around the mother board and you should find it. On rare occasions I have seen the mounted off the board but its very rare. note books are very difficult to take apart, so if you might be well served to take it to a dealer who knows how they come apart.