Cannot access CFE prompt

Hi

Could someone help please

I have an R8000 running stock firmware (V1.0.4.18) and I am trying to convert it to DD-WRT which I have been running o another router for the last few years

I try and flash the router via the web interface I get an error reporting that this version is not compatible. After some research I have connected up a serial cable to flash the router via this method.

My problem is trying to get to the CFE prompt. I have restarted the router started pressing the CRTL+C before, after and during the startup and I have been totally unsuccessful at accessing the prompt. The router just starts normally.

I do get to a # prompt but this will not allow me to run nvram or start the tftp server

Could someone help