What started off to be an easy upgraded turned into a nightmare and I have no more ideas on what to do. My Goal upgrade my 250gig 5400RPM to a 1TB 5400RPM or 7200RPM (3Gb/s) What I have done thus far. (Just to save me some typing every time I started an install of my OS I reformatted and performed a permission check and repair on the WD HD that I was installing just to be safe.) Gray disc is the system install disc that comes with your MAC for factory install. 1. Purchased a 1TB 7400RPM from OWC and CCC my HD, which worked great but ran really slow. The HD was flashed from a 6Gb/s to a 3Gb/s and I was told to do a fresh install. Ok not problem right, wrong. 2. Ran my Gray disk on my internal install error. (Ran disk internal) 3. Ran my Gray disk on my external install error. (Ran disk internal) 4. Ran my Gray disk on my external install error. (Ran disk external optical drive.) 5. So I returned the HD thinking it was the HD because OWC nor myself could figure out the issue. 6. I reinstalled my original HD and it runs great. CONFUSED AS HECK! OWC sent me two HDs and both had the same issue. Notes: each install took on average between 3-6 hours before the error would show up. Third HD WD 1TB 5400RPM 3Gb/s 1. Install the HD and reformatted (everything is correct on this part as I double check my settings and my portions is GUID) 2. Ran OSX 10.6 Gray disc install error. 3. Now since that failed I tried it again and same error. 4. Now I am running the Gray disk on my external optical drive and it took five hours but I was three quarters of the way completed before I received the fail install error again. 5. So I went out and purchased a brand new optical drive and same issues. 6. I installed my Gray disk to a flash drive and ran the install same issues. I purchased 10.6.3 from the MAC store, which did not work, and I ran it through the same process as the WD 1TB with no luck. I have my original HD installed and it works like a champ. I called OWC and they said I may need to replace my SATA cable but I told them I am still using my MAC with the original HD as we speak. He was confuse they are confused as well. I spoke to the APPLE Tech guys over the phone and theyre confused as to why I am unable to install the HD. I live about an hour and a half away from an APPLE store so I am trying my best to figure this out. If I need to replace the SATA cable I am more than capable is its a pretty easy fix but is there away to test it? Or can anyone lend a hand with some better ideas. My next step now is to CCC the drive via USB, install it within the laptop, and run 10.8 install on it and see if I can reformat it that way with a clean install. I am out of ideas as this has been an on going issues since last week, sorry for any grammar errors and misspellings. Please Help!