jakobud,
get to work early in the am,,get a bootable cd with memtest86 on it.
1. boot the (linux)cd and at command prompt type in memtest
let it run for a couple hours.
,,,if this results "OK"(no red blocks)
2. Put a different keyboard on this pfSense machine as someone else mentioned.
3. restart pfSense machine.
Post your results so someone else will know what has been found.
Take Care,
BC