Hi, I have a weird problem on my Macbook Pro Mid 2009. Whenever I try to launch my OS when my HDD is inside my Mac, I can't boot the system because I can just read the files on it but not write in it. The problem is not the Hard Drive because it works perfectly when I try it in the USB port. The weird thing is that when I put a Hard Drive inside my Mac that doesn't have an OS I can write and read on it... but If I try the same with a Hard Drive which has an OS I cannot Write on it just read the files that are inside (Even if boot the OS vie USB I can just read the files of the internal Hard Drive but I cannot write on it) My problem is that I don't want to boot my OS from the USB because the speed of the Hard DRive is much better when is connected with the SATA cable. My possible solution is to buy another SATA cable, but I'm afraid that it won't solve the problem since I can read and write files through it but just when the Hard Drive that is connected doesn't have an OS installed on it (which I find quite funny). Does someone knows which could be the problem? My Hard Drives are these ones Hitachi 160Gb (With Snow leopard installed) I can boot it via USB but not when I connect it via SATA I can't read not write files. Seagate Momentus XT 500Gb (With Lion installed) I can boot it via USB but when I try it via SATA I can only read my files but I cant write on it... so I can't boot the OS via SATA Toshiba 640Gb (With no OS installed) I can write and read files perfectly when I connect it via SATA, but I can't instal the OS here (which I found really weird) >_< Please if someone has a possible solution, let me know, I would really appreciate the help. ---------- Sorry I wrote the title wrong... I meant that I can't write on my Hard Drive... but I can read all the files.