Can't get System clock to be PLL out with input source as HSE, system crashes?

Hi folks,

I'm trying to initialise system clock to 168MHz without using cubemx generated function just to get better grasp of the RCC , PLL and clocks. So currently I'm trying to use HSE as source for PLL and PLL out as System core clock, right after setting the clock switch bits in RCC->CFGR, controller crashes.

Attached below is the function.