Windows 7: Shut down computer, remove all power sources, hold down power button

Why does shutting down the computer, removing the AC Adapter, removing the battery (if it is a laptop), and holding down the power button for 30 seconds fix problems in one's computer. I was recently corrected in a post of mine that this does not actually do anything unless one removes the 3 volt battery from the motherboard, but I know this is not true from experience. Here is the correction I am referring to from a more experienced member:

The reason I know that doing the hardware reset I described initially works:



1. I have a laptop that occasionally suffers from a USB Device Error issue. Every port gives me the message that the USB Device Is Not Recognized. If I follow the steps initially outlined in this post, it fixes my issue. I have done this at least 10 times.
2. My roommate a few years ago was unable to load Windows from his brand new laptop after just six months of owning the machine. The screen would not even show the BIOS options. We tried a half dozen times to get it to load by turning it off and back on. Finally, I turned it off, unplugged the AC adapter then unplugged the battery, and held down the power button for 30 seconds. Plugged the battery back in, plugged the AC adapter back in, and presto, Windows ran like nothing had ever been wrong.
3. I have been doing troubleshooting with my girlfriend's laptop and her family's computers (four laptops and a desktop) and have fixed all four laptops from various boot issues and crash issues using the method that apparently does not perform any sort of reset.

I have asked computer people why the method works; I have asked electrical engineers why the method works. The only answer that makes sense to me is an electrical engineer told me that holding down the power button with no power going into the machine allows the capacitors to drain by closing the circuit. I have yet to get an entirely satisfactory answer other than it performs some sort of hardware/BIOS/CMOS reset, which apparently is incorrect.

So is it magic? Or does someone out there actually know what it does?

Further information; this is what my manufacturer of my laptop suggested for my USB issues View Document. After step B. of the power cycle directions, my computer works fine.

Edit: I have skipped all the steps prior to the power cycle, and it still fixes my problem. It is not a software update that is fixing the problem.

Okay, so here are my theories, and I want someone to correct me if I'm wrong because I really do want to know how this works in case people ask why I'm suggesting they do a power cycle. My theories are:

Removing all power from the system, minus the 3 V battery powering the CMOS, causes one or two of the following to happen:
A. The BIOS resets because ~3 V is not enough power to maintain it.
B. The BIOS and CMOS chip are designed to reset if less than say 3.5 V are powering them
C. The rest of the system is completely devoid of power, so there is a hardware reset in the sense that no
components are able to run, and so no power memory remains in components to cause them to continue
working incorrectly. Thus, when the computer is given power again, components not powered by the 3 V battery
are reset to their original working condition.

Agree, disagree?

Edit: I looked into this a little more, and I'm wondering now if this might be due to RAM being corrupted, and a simple power cycle (turning off the computer, waiting 10 seconds) does not clear the RAM as completely as removing all power and doing a full power cycle.

What that does is removing static electricity from the system - it is like grounding the PC.

Actually, I just found out what it does. It removes the power from all components, as I mentioned earlier, but the affect of this is that the software interfaces between the BIOS and the hardware are severed and then the BIOS reestablishes those software interfaces between the BIOS and hardware when the computer is reconnected to power. This is coupled with the clearing of the computer's temporary memory. That way, if one of the software interfaces between the BIOS and hardware is malfunctioning, it is reset.

Rather interesting. You can read about it on Use Hard Reset to Resolve Hardware and Software Issues HP Pavilion dv5000 Notebook PC series - HP Customer Care (United States - English), and this makes perfect sense as to why so many computer problems can be fixed with a hard/hardware reset.

Good find.