EDIT: OK, so I've worked out that the new HD is the problem, as miniConvert and NewMacbookPlz mentioned, it looks like a permissions problem. So what's the best way of fixing this: a) Reclone my drive using SuperDuper (again) or Carbon Copy Cloner? b) Restore from Time Machine backup? c) Repair permissions from my working HD (is that possible?)? I really appreciate everyone's help so far - I think this is close to being solved! Original: I have just installed a new HD and 2x2GB RAM into my late 2007 2.2GHz MacBook. I booted my laptop, and it all was going fine, however no apps will work - they all crash at launch. The HD seems to be fine, I can view all my files in Finder, etc, but no apps. I reinstalled the original RAM, and same thing, so I'm now typing this from my iPod touch. What could cause this? How can I fix it? It seems strange the computer will boot, but won't launch apps... The new HD is a clone of my old one using SuperDuper. Please help - thanks in advance!