1) Test the AC adapter (Charger) first.http://www.itsbattery.com/gateway-ac-adapter/Gateway-ID49C-AC-Adapter.html
Test with a multimeter.
(An economical multimeter can be purchased for as little as $5 to $12. Available in a multitude of stores. An auto parts store is but one example. Checkout aisles of major discount stores, may have them on the rack)
Function knob set to DC Voltage.
(If just a symbol the symbol is a dotted line over a solid line)
If more than one DC Voltage scale set it to the 0 - 50 Volt scale.
Positive (Red) probe lead of multimeter goes to the Center Hole, of the plug end that plugs into the laptop.
Negative (Black) probe lead touches the cylindrical metal shell, on the outside of the plug end.
You should be reading 19 Volts DC.
Also have an assistant gently wiggle the cable from AC adapter to laptop, and power cable to AC adapter (Charger)
Fluctuation in the reading means you have broken wires.
AC adapter checks out OK?
2) DC Power Jack:
The DC Power Jack is the jack on the laptop, that you plug the AC adapter (Charger) into. (DC_IN)
Battery removed, (And AC adapter, 'natch), use a No.2 pencil, and with the eraser, gently see if you can move the Center Pin around.
ANY perceptible movement means damage to the DC Power Jack, and replacement.
3) AC adapter and DC Power Jack checks out?
Problems with the Power MOSFETs used in the power section, on the motherboard, or possibly Ceramic Capacitor failure.
(Multi-Layer Ceramic Capacitor, and they are Surface Mount Devices)
Using the HP Pavilion dv6000 series, and Pavilion dv9000 series of Notebook PC's, as an example,http://mayohardware.blogspot.com/2010/04/important-parts-on-dv6000-and-dv9000.html
Looking down at the second photo with the Alpha and Omega Semiconductor - AO4407 - Power MOSFET circled in Yellow, look at the small rectangular shaped object to it's Right. Has a wide dark band on it.
This is a Ceramic Capacitor.
There is one above it of the same size, one above that one, and one to the right of the top one.
If any one of these, or the Power MOSFETs are blistered, blackened, or bubbled, they need to be replaced.
Due to issues that could arise by replacing, and having more components be bad, or go bad; the logical choice by most tech's is to simply replace the motherboard.
(Also puts more dinero in their pockets)
[ Your user name reminds me of Hee-Haw. "If it wasn't for bad luck I wouldn't have any at all." Lol!
Hey...........it's going to get BETTER! ]
For additional questions please post in a Comment.