A couple of notes on clearing the BIOS settings in the CMOS memory.
If the computer is plugged in and getting power, removing the CMOS backup battery will NOT reset the BIOS settings.
Even with power unplugged, it can take half an hour or more for the voltage to drop low enough for the CMOS memory to reset.
If you want to reset the BIOS settings, it is always best to set the Clear CMOS jumper and then press the power button. Remove the jumper, and then start up and set the BIOS settings.
As noted in another answer, a weak CMOS battery can cause some very strange and intermittent problems. At 9 years old, the CMOS battery should have been replaced at least once by now.
For most systems, there are only a few BIOS settings that you need to be concerned with.
HDD and Optical drive detection.
Boot order
Num Lock Status
Date and Time.
If your system has onboard video, and you are using an alternate video card, you may need to set a video option.
If the system has been running properly, and then started having problems, flashing the BIOS is not the answer.
Looking at the HP information on this 9 year old computer, my first thought is that you have a hardware end of life or failure issue.
Take a look at this website to see pictures of damaged motherboard capacitors.
http://demo.techmetric.net/hardware/pc-build/16-pc-motherboard-repair-blown-capacitors.html
I suspect that you will find at least one bad capacitor on the motherboard.
Also, after 9 years, of software installations and Windows updates, the Windows installation might have enough bad links and corrupt settings to cause the system to slow down significantly.
And as you only have one year of security updates left for Windows XP, it just might be time to put time and funds into a new computer rather then trying to get a little more out of this one.
Chas