This sounds like one of five things to me.
1. A faulty charger
2. A faulty Battery
3 A possible I/O daughterbord failure (if one exists in this model)
4. The motherboard could be suspect if there is no I/O daughterboard in this model.
5. Bios issues (Low level software in charge of monitoring battery levels among many other things)
Lets start with some simple things first. Will the computer run with only the charger? If yes that is great news. If No. Dont panic!
If the computer Runs well without the battery then we could very simply be looking at an issue where the battery in this laptop is "giving up the ghost" So to speak. In this scenario I would suggest getting an HP OEM battery as a replacement. Nothing used, nothing compatable. this will ensure better warranty coverage if anything is to happen.
Lets keep troubleshooting though to be sure we have exausted all aspects.
Now that we have an idea how the computer performs without the battery. Lets try to get a simple bios upgrade done on the computer to see if this resolves any of the charging issues. This is a little bit of an advanced teqnique that is as simple as running a file most times but can terminally destroy your computer if done improperly. Myself nor this website will take responsibility should you choose to go this route. You have been warned!
The first thing to do is to identify your product number. Here is a link that HP describes how this is done. You will need this to find your correct bios version.
http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/kb/docDisplay/?sp4ts.oid=432999&spf_p.tpst=kbDocDisplay&spf_p.prp_kbDocDisplay=wsrp-navigationalState%3DdocId%253Demr_na-c00033108-57%257CdocLocale%253D%257CcalledBy%253D&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken
With Product number documented we now go to the hp support site to find your drivers and downloads. Please find the HP support Page Below:
http://h10025.www1.hp.com/ewfrf/wc/siteHome?cc=us&lc=en
Once there type in your product number and click the go button. This will take you to a page that offers driver downloads and such. Your new bios will be located under the drivers page.
Here is an example of what you will see but please do not use the drivers from this page as it may be the incorrect model and damage your laptop.
http://h10025.www1.hp.com/ewfrf/wc/product?product=435618&lc=en&cc=us&dlc=en&lang=en&task=
I would like to take the time to point your attention on the bottom right of the screen where HP defines: "
HP expanded the battery pack recall on May 26th, 2011. Click here to validate your battery."
It looks like this model did infact have a battery recall at one point and you may be feeling the sting of not taking advantage of this while it was an option. Moving on.
Next select your Operating System from the dropdown list. Due to the age of the computer I imagine you will have Windows XP.
Once selected, you will now be able to scroll down and identify a spot to expand a tree for your bios version for your specific laptop. Download this file and be sure to remember where to save it. Simply run the .exe file that downloads and follow the onscreen instructions. Please be sure to keep your laptop plugged in and if you can make sure the battery is as charged as possible. Walk away from the laptop and come back after some time. You do not want to be the impatient one that reboots their laptop because you didnt think it was working as fast as it should. This will leave you with a very pretty paperweight.
Hopefully your computer has rebooted and my windy instructions havent lost you. Now that we have an up to date bios, is the computer acting any better? if not, we are quickly moving into a direction (if we havent already) that it would be time to take your computer into the repair shop. They will be able to identify for you if the computer has an I/O daughterboard that can be replaced. If it does not I am sure that with an up to date bios and a brand new battery that the motherboard may be failing. Due to the age of this computer, it may be time to replace it. If you have followed these instructions, I assure you, you have put in a valient effort!
Best of luck!
-Rogue