My mac will not start up so I am trying to view the files on my mac through an external HD
Troubleshooting: My computer won't turn on
Read and follow all the steps.
...before changing memory I first need to copy the files from my mac to my ext HD
A backup is always a good idea, but there is no need to do that prior to changing RAM. Your hard disk's contents are not dependent on it.
Retrieving data ...