HP Pavilion 8650C won’t access setup

HP won’t access setup/frozen on HP Blue Screen.
I am working on an HP Pavilion 8650C, When you start the pc it automatically goes to the HP Blue Screen and stops. I have pressed escape and then F1 (for setup) noticed it checks the RAM, CD, DVD, CPU, then says its entering setup and never gets there. I also have to plug the pc in to turn it on and unplugg it to turn it off. What could be wrong with it and how do I fix it? Th problems could be separate issues
Is this a case where the systemboard needs replaced along with CPU and RAM? Is it worth going to the expense? Thanks to all who answered the first part of the question, I could not respond to get anywhere so I am resubmitting the question.