I recently encountered a quite strange behavior of my HP 6910p computer. It became extraordinary slow if hooked on the charger. By slow I mean that Windows booting up took more than half an hour (I tested this only once :) ) and afterwards Task Manager showed 100% CPU usage for both cores all the time, no matter if no userspace program was running. This itself could have been a simple Windows issue, but essentially the same happened for a Linux Live CD, and even worse: the BIOS menu was definitely slow to respond. However if I removed the charger (so that it ran on battery), everything went back to normal.
Realizing that this is a hardware problem I had it repaired under warranty (they replaced the motherboard), after which everything went normal for some days and then the issue reappeared. This happened during the weekend (obviously) so I had to do something. What I noticed was that by moving the cable of the charger sometimes it can be healed. So the resolution was simple: the wire is broken somewhere. But which wire? I have never noticed a power failure, meaning that only the third one in the middle can be the source of the problem. Yes, recent notebooks demand a charger with an additional line which might tell if the charger is a proper one or not. If this connection is not present then the power management of the notebook must fall back to some extra low profile rendering the CPUs slow and the computer essentially useless.So apart from saying a big thanks to HP I only could cut the wiring open and resolder this inner wire after which I applied a plenty of thin teflon tape to prevent it from either breaking or shorting to the other ones.
Now everything is back to normal, the long-term solution however is buying a new power supply.
