I have a 3 year old Acer Travelmate 4061 laptop which has been working fine until few months ago. Whenever I booted to Windows XP - the keyboard just wasn't responding and I noticed on the task manager, the CPU usage is always almost 100% and I can't work out which processes that causes the CPU usage spike.
Strangely enough, I didn't have this problem when I booted to Linux (Ubuntu).
I could've just use Linux and not bothered with this problem however I was preparing for my SCJP certification and the 2 exam preparation softwares that I use don't run on Linux (a little bit ironic if you think about it, Java is supposed to be cross platform yet these exam softwares were created using M$ technologies which only run on Window$). Yes, I have played around with WINE, however not having too much success with it.
I have taken some drastic measures and wasted lots of hours in trying to figure this out and ranging from killing processes, attaching/re-attaching USB devices to the obligatory a couple rounds of XP re-install.
Luckily the certification softwares most of the time only require mouse clicks (my USB mouse works fine) and when I really have to use some keyboard input, I had to resort to Windows On-Screen Keyboard.. Uhm you don't know what an On-Screen Keyboard is? Go to Accessories > Accessibility > On-Screen Keyboard, not the fastest for keyboard input but it works in this case.
Trolling through Google search results wasn't pointing me to the right direction. Some of the result suggested that harddisk might be the cause of this problem. And I actually did believe that, although I can't work out if this was the case then why Linux is running fine.
Battery is the source of all evil
After having to live through this experience for a few weeks - I had some sort of divine AHA moment. I ran the laptop on power supply and remove the battery and lo and behold the CPU usage drops to normal!!
Googled around using battery as one of the keywords led me to search results that confirmed the problem. This particular post is particularly useful: http://www.tim.id.au/blog/2009/03/11/solved-100-cpu-usage-on-acer-aspire-1640z/
In the link above, Tim described in details steps he had taken to figure the problem out (more sophisticated then my endless trial and error). I also later found out that by disabling the battery management from device manager also fixes the problem. I can't remember exactly what it is since I am not on my laptop at the moment.
Update: As per Tim's request, you can fix the problem without unplugging the battery by going to Control Panel > System > Hardware > Device Manager. There should be a node called Batteries - expand that, you'll see Microsoft ACPI - Compliant Control Method Battery. Right click on it and disable it. Screen shot below: [caption id="attachment_278" align="alignnone" width="386" caption="disabling battery management in Acer Travelmate 4061"][/caption]
My confidence in Acer laptops has been tarnished now. But on the other hand I haven't had much experience with laptops - perhaps this is common problem.