While working, at random times, the keyboard just disappears. No way to type anything in, no cursor. Only the mouse keeps working.
The way I deal with it now is ending the KDE session (with the mouse) and starting a new KDE session.

I haven't been able to associate it with specific actions. It seems to happen randomly (or at least I haven't found any event linked to it).

My current keyboard is a Dell USB Keyboard.

# lsusb -v

Bus 004 Device 003: ID 413c:3016 Dell Computer Corp.
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 8
idVendor 0x413c Dell Computer Corp.
idProduct 0x3016
bcdDevice 0.09
iManufacturer 0
iProduct 2 Dell Premium USB Optical Mouse
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 34
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xa0
(Bus Powered)
Remote Wakeup
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 1 Boot Interface Subclass
bInterfaceProtocol 2 Mouse
iInterface 0
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.11
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 83
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0006 1x 6 bytes
bInterval 10
Device Status: 0x0000
(Bus Powered)

possible causes i know are:

(a) low power supply that suddenly turns keyboard off
(b) electromagnetic interference
(c) bad keyboard wires
(d) bad connection to the PS/2 socket
(e) bad motherboard or bad keyboard controller
(f) bad keyboard in general

Do "dmesg | tail" to know what actually happened when the keyboard hangs (of course after the keyboard functions back).

Or just create a script with the following code in it so that you can just click it with the mouse. Save this to a script with executable flags set and put it in the desktop or anywhere the mouse can reach.

Oops my bad. It's usb so it could be a bad usb connection and not PS/2. Sorry 'bout that.

Thank you, konsolebox. I'm starting to rule out some of the causes:

(a) low power supply that suddenly turns keyboard off: I have a UPS. Not even a flicker.
(b) electromagnetic interference
(c) bad keyboard wires
(d) bad connection : Checked. All fine. Plus, it consistently gets fixed after reboot or on new X session.
(e) bad motherboard or bad keyboard controller
(f) bad keyboard in general

As for the log, I didn't see anything out of the ordinary before my initial post, but I'll run the script as you recommend.

You may try to add this in "ServerFlags" section in xorg.conf:

Strange, this just began happening to me the other day as well.

I can still switch VT's and kill X, but I cannot use keyboard shortcuts or type into any text box. Switching to an empty VT and killing off lingering kde processes will let me log back in, but it is irritating. This doesn't happen with OpenBox on the same machine.

I don't know if you've figured it out yet, xri, but on my system, issuing a kill -9 on the pid of kded4 will restore use of the keyboard minus the keybindings. Of course I have to switch to a VT in order to do this, but upon switching back I can resume 'normal' work.

No what I mean is the internal power supplies from the Power Supply Unit. External current won't really affect it since most PSUs contain large capacitors.

Oh, I see. My bad. I'll keep using your check list for my system.

Sounds like a software issue then. I take it you don't see anything in /var/log/Xorg.0.log? Just to verify, it's not a wireless keyboard, is it? If you want to cheat, maybe try running a live CD from another distro and see if you have the same problem. If it works properly see what's different in your xorg.conf files and tweak your Slackware one accordingly.

Thank you all for your input. I'll keep looking into it and post accordingly.

I'm giving closure to this thread.
The keyboard freezing consistently occurs while using rdesktop with one particular service I use, when I inadvertently press the Shift or the Ctrl key while working in that program.
I deactivated all the slow keys and sticky keys activation on Kcontrol. After that, I've never experienced this problem again with my keyboard.

Thanks a lot for your help.