Those three things you mentioned, and the processor should be the only necessary components you need to at least get the system to post... If you aren't getting any beeps what-so-ever and not getting anything to display on the screen, it could very well be the processor... I'd test that out first if you have another processor around that you could pop into that system. How much RAM is in that system? If you have more than 1 stick, try only using 1 stick... Stick with min requirements
-SlickVic78