I recently replaced a bad lcd cable in a Compaq Presario C700 for a friend. When I booted it to test the display everything worked fine for about 20 minutes and then it shut off. I initially thought it was a cooling issue because it was running pretty hot. I let it sit for a couple hours and switched it on again. It ran for 5 minutes and then shut off. I went to plug the power supply into the laptop and the power led wouldnt even come on. When I took the plug out of the laptop upon closer inspection I realised that I could here a slight crackling noise when playing with the plug on the power supply. There was apparently a short in the power suppy that neither of us were aware of. I went to try a working power supply by the exact same company and it was the same voltage rating and it wont even show that it is recieving power. I opened it up and there is no visible damage to the board and the jack itself is firmly connected. I need some troubleshooting suggestions as far as how to narrow it down further from the jack, battery, and motherboard preferably least expensive to most. I have access to all replacement parts individually and have the technical knowhow to replace them.