I have lost the keyboard in my user account. This happens only when running kde as user so the problem is obviously in the ~user/.kde settings. I'm pretty sure I can fix it by moving ~user/.kde to a backup then restarting but I will then have to re-do all the user settings, bookmarks, mail, addresses, etc.

The easier way would be to just replace the appropriate file.

Does anyone know which ~user/.kde/config-file might cause loss of the keyboard?

Another probably related issue....I'm pretty sure this was caused by a hardware-related freezup...this computer has been afflicted with STLS (sudden total lockup syndrome) since I got it....probably the reason the P.O. sold it!.....and I have concluded that it is a faulty hardware issue.

Memtest says the memory is OK so I guess that leaves either HD, CPU or motherboard.

Which is the most likely and how do I check it out?

Symptoms are...computer totally freezes, no mouse, no response to keyboard, must be reset by using the power-off reset. No hint of approaching problem, no error messages, problem leaves no trace on restarting. It is a dual boot system (actually triple boot...Debian Lenny, Win XP, and an old Kanotix system) and STLS has struck in all systems so I think it must be a hardware issue. Only semi-consistent hint is that it most frequently hits when copying a DVD or when plugging in a usb device...but it has hit at any time, even when the computer is idle.

I had a similar problem.
First thing is to upgrade the power supply.
These new double-core motherboards can be real power-hogs.
If you're using an older motherboard and the power drain is not an issue - take a good look at these small capacitors, located all over the MB. I some of them appear to be "popped" or leaky - you may have to replace the MB.
I bought an Asus MB in 2002 and 2 years later all these little capacitors popped. The PC worked but once in a while it would freeze, just like yours does.
good luck!

Sounds like the best hint I have yet.....it is an ASUS computer about 4 years old.