First the above poster is correct you have a hardware failure not related to RAM. To fix this you can either start changing things willy nilly and eventually get it working again or go about things in a professional manner.
The first thing to do would be to get a copy of the HDD makers diagnostic tool and test your HDD/s.
If there has been nothing new added to this unit then you can get a copy of the Ultimate Boot CD available at
http://www.ultimatebootcd.com/download.html
Make your computer boot off the CD as first option and then run the diagnostics to see what is going wrong. With this CD you can test all of your hardware and find any faults.
Col