I installed ML on my MCP 2010 within a few days after ML premiered. I did not do a clean install of ML and ever since then gradually over time I have noticed that my system slows down a lot and native Mac applications hang and freeze, etc. The educated guess I'm running with is that the problems I am experiencing are because I didn't do a clean install of ML. Now with performing a clean install, I know I need to wipe and reformat the HD. However, I hesitate to do this right away for a few reasons: 1. I had my MCP appraised for trade-in value a few months ago and part of that procedure requires that their techs test the machine. They informed me that everything was fine "except" the HD has one corrupt data block which was enough for them to not consider taking my MCP for trade-in. Up to that point, I had no idea because the MCP had always worked great for me. 2. I do have a backup external HD attached to my MCP at all times that regularly makes backups using Time Machine. I am concerned, however, about the health of the external HD and whether or not it is potentially corrupt as well. I need to verify somehow if all my data is indeed safely backed up on the external HD and if all that data can also be safely retrieved. I need to verify the external hard drive before I officially wipe and reformat the main drive of my MCP. I did actually run the Disk Utility app on the external HD, and it reported the following in red text: ... Invalid sibling link The volume MyPassport was found corrupt and needs to be repaired. Error: This desk needs to be repaired. Click Repair Disk. I do not, however, want to simply click Repair Disk until someone can tell me if this is safe to do or not without damaging the data. Finally, just to be safe because the current internal drive has one bad block, I decided to place an order for a new 512 MB SSD and 8 GB RAM. I received these parts in the mail. I plan to simply wipe and trash the current HD in my MCP and install the new SSD. In short, I am looking for expert advice on a procedure of steps to follow for installing my new SSD and RAM, installing clean copy of ML onto the new drive, and while safely preserving my personal data on my external backup HD.