I added 4Gb years ago to my standard Mac Pro amount, using 6Gb in total, working perfectly Yesterday, I returned home to a blinking power light which was new to me. I tried running on your 4Gb only, with original 2Gb removed. No way to diagnose when unable to boot. Same problem. I tried the original 2Gb and all's working, but too little to get on. What can I do with the broken sticks? Can I try on at a time to see if one was damaged and the other is fine?
First of all I'm sorry to hear that you are having problems with your memory module.
As you have tested each module one at a time in the system and the 4GB is not working on it's own it does look like it's faulty and we can arrange an exchange for you. To arrange an exchange please contact our customer service team directly HERE who can set it up for you.
All our memory modules have a lifetime warranty so we can exchange it for you no problem at all.