Thanks for the reply.
This laptop has a standard US style keyboard. The ; key is at the right side of the L key, so it is not that near the space bar.
As mentioned in the first posting of this thread, my "v" key also displays "v4", the same for the "4" key, it also shows "v4". Very weird.
I have checked the laptop for viruses with MS Security Essentials and it is clean.
The BIOS has been updated to the latest level too. My next try will be to use the laptop's recovery disk to reinstall it from scratch.
BTW, I'm replying to this thread from another computer, as it is a big pain to type from that laptop with such a problem.