i do not understand why there is no need to have an new kernel for an old computer, as there are a lot improvements related to various filesystems (including performance), power-management, drivers…the list would be too long.
This is clearly the opposite of Linux philosophy in my opinion, the ability to have bleeding edge system on older computer.
@sktelios You could even have a more responsive system with XFCE or Openbox (thanks to Mabox).
KDE is quite slow on old computer even if the memory footprint is reasonable.
Now, regarding your issue, you could start reading this