Keyboard doing Strange Things

April 25, 2009 at 11:36:20
Specs: Windows XP SP2

I'm fixing a problem on a family members computer:

The keyboard doesn't respond to all keys. It responds to some (a few from the alphabet, half the arrow keys, etc). They've tried two different keyboards (one PS2, one USB) without success. Even in BIOS, the computer doesn't respond to all keys. They say they had a different computer repair person come out, do a cleanup of the system, and it worked for a bit after that, then went back to ignoring keystrokes.

To me, except for the other repair fellow, this seems like a hardware problem. What do y'all think? Have y'all heard of virii causing this kind of trouble even in BIOS?


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April 25, 2009 at 12:29:18

Problems like you describe are almost always caused by a defective keyboard - stuck keys, or a cheap one that has been used a lot and has worn out some of it's contacts, or a corded one that has some wires broken inside it's cord.
If that's the case, the keyboard won't work properly on any computer - have them try the keyboards with another computer, or try a third keyboard with their computer
Cleaning up the system physically would probably have no effect, but checking connections might.
They could try making sure the main connector from the power supply is properly seated in it's mboard socket.

It's extremely unlikely there'sanything wrong with the USB or PS/2 port, and even if there was, it's almost impossible for both to not work properly at the same time, unless the power supply is failing and is not able to supply enough 5v voltage or current - in that case other USB devices and CD and DVD drives won't work properly either.
Have them check your PS voltages in the bios.
See response 4 in this:

Of course, if the keyboard is a "combo" one that can be used with either a USB or a PS/2 connection, if it doesn'r work properly when connected one way, it's not going to work properly connected the other way either.

A USB connected keyboard may not work properly when connected to certain USB ports, but in that case it usually works fine or doesn't work at all.
See response 3 in this:

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April 25, 2009 at 12:50:58

So, verify that the problem is not the keyboard by testing it on a different computer; trying a different keyboard on the target system, etc.

Failing that, check PS voltage in BIOS for dead/dying PSU, even though we'd expect other system troubles if that were the problem.../check_other_areas_of_the_system_for_trouble

Failing that, burn the computer to the ground, and resurrect it in a different machine.

(Odd semi-forgotten addition: they have a PS/2 mouse which continues to work fine; which does kind of interfere with my original thought of 'its something wrong inside the computer'...)

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April 27, 2009 at 20:41:03

The most likely thing is a defective keyboard - other things don't usually cause only some keys not to work.

The PS/2 mouse uses different circuits. If there were a voltage/current problem, a PS/2 mouse usually requires less current, so sometimes it works okay when the keyboard doesn't.

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