I'm running a three year old HP Pavilion zx5000 notebook. Starting a few days ago, it's randomly been ignoring the its AC power. Without touching the cord (it's firmly in and not loose) it will suddenly go over to battery power. Sometime, unplugging the cord and replugging it in will return it to AC power, however, this now rarely works.

The problem does not seem to lie with the battery (although I am currently testing it without the battery). I have tried two different batteries--sometimes the machine will recognize the battery and begin recharging while turned off but then immediatly switch to battery power when turned on; other times it will boot up on AC power and then switch to battery at random intervals; other times it will refuse to recognize AC power at all and will neither charge a depleted battery or allow the machine to turn on. These different circumstances do not seem to follow any sort of pattern.

I took the machine apart to ensure that it wasn't overheating due to dust (I have one of the last Pavilions to use a Pentium 4). Sprayed a little compressed air around and generally cleaned it out, to no avail. The outlet is working fine and I'm opperating behind a surge protector.

Got any ideas? I really need to get this fixed: it's impossible to be in college without a computer. I'd appreciate any help.

Yup, definitly not the battery-- after about 30 minutes running off AC without a battery, the machine lost power and turned off.

Check the solder on the power port. A lot of laptop owners dont realize is that the most dangerous part of the lappy is the power port. They either get loose off the solder, or just barely hang in there.

Solder looks good.

could be that the port itself is damaged in some way. Make sure it fits in the port snug, not wiggly or anything. If not I might say try a different power adapter.