Connecting my macbook pro as external monitor to my imac

How do I connect my old imac (20” early 2008) to my old macbook pro ( 15” late 2008), to use the latter as the external monitor? You see, my imac has the black screen problem on start-up which is not resolved by pressing command + option + R + P. When I do this, the screen becomes white for a second then goes black again but the computer is still running. I want to access my files on it and was thinking if I can connect it to my macbook pro and use that as an external monitor instead. What cables do I need to do so & what keys do I press on the macbook pro once connected? Thanks in advance.