crash after overclocking

Hello,
Seems I lost the game : I tried to overclock an old AMD K6-II 300 MHz to 450 MHz using the MB BIOS options, and this PC isn’t booting any more since then : not even the BIOS.
I know many depends on my MB but is there some trick to make the way back ? Or did I lose this MB or CPU ?
Thanks for replies and best wishes for the new year.