F4-key mysteriously reassigned

Question

In the middle of today, my F4 key started producing the letter p, without my conscious acting and I can't seem to revert this change. Whenever I press F4, p appears instead. How can I change this back?

Pressing p, xev returns:

KeyPress event, serial 38, synthetic NO, window 0x4400001,
    root 0x150, subw 0x0, time 581565, (696,-17), root:(698,55),
    state 0x0, keycode 33 (keysym 0x70, p), same_screen YES,
    XLookupString gives 1 bytes: (70) "p"
    XmbLookupString gives 1 bytes: (70) "p"
    XFilterEvent returns: False

KeyRelease event, serial 38, synthetic NO, window 0x4400001,
    root 0x150, subw 0x0, time 581605, (696,-17), root:(698,55),
    state 0x0, keycode 33 (keysym 0x70, p), same_screen YES,
    XLookupString gives 1 bytes: (70) "p"
    XFilterEvent returns: False

Pressing F4, xev returns:

KeyPress event, serial 38, synthetic NO, window 0x4400001,
    root 0x150, subw 0x0, time 582298, (696,-17), root:(698,55),
    state 0x0, keycode 33 (keysym 0x70, p), same_screen YES,
    XLookupString gives 1 bytes: (70) "p"
    XmbLookupString gives 1 bytes: (70) "p"
    XFilterEvent returns: False

KeyRelease event, serial 38, synthetic NO, window 0x4400001,
    root 0x150, subw 0x0, time 582318, (696,-17), root:(698,55),
    state 0x0, keycode 33 (keysym 0x70, p), same_screen YES,
    XLookupString gives 1 bytes: (70) "p"
    XFilterEvent returns: False

As far as I'm concerned, both keys appear to me as one and the same key. Where can I revert or change such low-level behavior?

Update: I plugged in an external keyboard for which F4 works as expected. So... is my keyboard broken?

Update: While in GRUB, before the kernel starts, F4 simply does nothing as opposed to produce a p. To me, this can only mean that it's an OS problem.

Update: In the ttys (1 to 3, 5 and 6 (I can't access the fourth through Ctrl-Alt-F4)), F4 equally produces p.

Answer 1

It's a long shot, but this can occasionally solve mysterious problems with laptop BIOSes. Switch off the computer, unplug it and remove the battery. Wait a bit, then plug it on. It's possible that some memory used by the BIOS has become corrupted and a complete power cycle will reinitialize it.