One of my HPaqs (Presario V2000Z) had a power jack issue. I thought the jack had become unsoldered, and that it was going to be a pain to fix. But it turned out to be the very end of the power cord that had a loose connection.
HP has been using the same exact power supply model for about 5 years now on their Compaq and HP lines, so it's very possible your power supply is the same model as mine and may have the same defect. I called HP and they next-day shipped me a new power supply (with only about 2 weeks left on my warranty).
It's nearly impossible to tell whether it's the power jack or the power supply without a second power supply to test it with (I used one from a newer HP).
If it's not the power cord, and if you know how to solder, it should be a very easy fix once you disassemble the notebook (which will probably be most difficult). There are a few possible causes for the failure however:
1) Solder points have broke and become disconnected. (simple solder job fix, no need for replacement parts)
2) Metal connectors have broke where it connects to motherboard. (you will need a replacement DC jack part, remove the old one, and solder on a new one)
3) Metal connectors inside the jack have broke. (same fix as 2)
4) Metal ring on which solder is applied has come off the board. (very difficult if not impossible to fix, time to get a new motherboard).
Since HP uses the same DC jack part on almost all their notebooks, you shouldn't have a problem finding a replacement part. I expect it's the same part number for all their modern notebooks.
Most places that charge $250+ for this type of repair don't bother soldering. They just order a replacement board. Very wasteful and lazy, since this type of repair job is fairly easy once you have the laptop disassembled.
If you have never opened a laptop before: Don't lose your screws. If you have a laptop with different sized screws, don't forget what screw goes where. (I usually take a piece of paper or cardboard, and draw a diagram of the bottom of the notebook, and then punch the screws through the cardboard where it goes on the diagram- that way I don't lose my screws and I know what screw goes where. Once I'm inside, I get another piece of cardboard and draw a diagram of the inside screw locations, and punch those screws where they go).
The worst laptop manufacturer is Gateway as far as screw sizes. HP and Dell are OK, only a few different sizes and easy to remember. Asus (particularly the EeePC) is a joy to work with since it only uses a single screw size for EVERYTHING.
Anyway, you should be able to break the laptop down to the motherboard. If you can't solder and don't know any friends/family that can, take the motherboard in to a small electronics repair shop in your area. Hand them the motherboard and the replacement jack. They should be able to see the problem and fix it for a reasonable fee, probably right there on the spot.
Good luck.
