Why does the CPU usage reach 100% when laptop is plugged in?

I have an HP Elitebook 8440p with Windows 7 Ultimate, i7 Processor and 8 GB RAM.

For the last couple of days, when I plug-in my laptop for charging, the CPU usage shoots up to 100% and remains there for around 15 minutes. No offending process shows up in Task Manager/Process Explorer but the laptop is practically unusable for that time. The CPU usage becomes normal when I remove the power cord but shoots up again when plugged back. This is happening with different power adapters/wall sockets so it might not be a faulty adapter issue.

Why is this happening and any pointer to resolve this issue?

Solution 1:

It might be that Windows does backup or hard drive scans while the power cord is plugged in, so look into back up management too see if there's something there. You could try booting the computer in fail safe mode to minimize the programs loaded and see if the problem persists.

Solution 2:

Take a look at All Programs, Accessories, System Tools, Task Scheduler. For each task listed on the left, look at the Conditions tab. Do any tasks have the following options ticked?

Power
Start ths task only if the computer is on AC power
Stop if the computer switches to battery power

You'll probably need to Task Scheduler as administrator to manually remove any tasks.