I also have an OWC RAM kit for my Early 2008 MacPro (which I'm still using ). One pair of the RAM sticks caused an issue with a blank screen on startup and flashing power light. I removed the RAM pairs one by one to find the offending set, and ever since I took it out the computer has been OK. I even got a replacement for those faulty RAM sticks from OWC under warranty, but after a few weeks the computer started showing errors again until I took the new sticks out. I basically just left them out from that time on, as I'm not sure if it's the OWC RAM causing the issue or those specific RAM slots or something else. Basically I've just been living with a bit less RAM in this machine rather than fight it.