use throttlestop and disable intel thermal frameworks if possible, other settings in bios might disable power limits but very likely there is a power savings mode enabled or it is bottlenecked by your gpu which isn'tt functioning properly which may have a power savings mode enabled in it's manufacturers controll panel nvidea/amd.
Edit: the TDP and the current power are completely different things so when you said 65watts I assumed that was the current which on newer processors is always above the TDP max, I assume this might still be relevant. If you have had the pc for years and it has never gotten slower then chances are you just have a slow CPU. There are still lots of fun games you might be able to play such as Arma 3 which supposedly uses only 1 thread.