Posted 20 November 2012 - 10:05 AM
I do a fair number of jobs like this.
By attempting to turn it on with a new drive attached, you probably flushed everything.
Make sure that no other drives or flash keys are connected to the computer. If you ever had other drives connected at the same time as the 'special' drive, they may have the data on them in things like paging files or backups. Make sure any optical drives do not have disks in them. Unplug the power and press the power button to make sure all power is drained from the capacitors in the system. Turn it on with no drive connected and let it give you an error then turn it off. Unplug the power then hold the power button in to drain it again.
Reading the data from the RAM usually requires you to have viewed the images and then within a short time after power is removed from the computer (some say 20 minutes for standard forensic equipment) pull the RAM and read it cold. If you have powered it on several times without looking at the images the RAM should be clean.
If you are worried about a well funded government or large media organization accessing the data, you must destroy the platters inside the hard drive completely or it can be at least partially recovered with things like spin stand microscopy techniques.
I advise my clients who are 'personalities' to never type, save or visit anything on a computer that they would not want to see their name associated with on the front page of the newspaper.
My lawyer friends say that the 'e' in email stands for 'evidence'.