回答先: ? Hard Drive on Start Up but boots from external hard driveYour hard drive is most likely dead if it shows up as Disk 1. If your MacBook Pro came with 10.7 or later, you can use Internet Recovery to get the OS back on it after installing a new hard drive. If it came with 10.6 or earlier, you'll need to install off the restore disks. However, you say you can boot off your external drive. Is that just a regular install of OS X, or does it a backup/clone of your internal drive that has failed? If it's a clone of your old drive, you can install the new drive than clone the external back to the internal. If it's a backup, or it contains a Time Machine backup, you can restore from that once you install the new hard drive. I have not provided instructions for every method I mentioned, but if you need help, let me know and I'll do what I can to walk you through the process.
回答先: ? Hard Drive on Start Up but boots from external hard driveMake sure you'r MacBook is completely powered off. Press the power button, and then press and hold the ALT key. After a few seconds, you should see a selection of icons that will let you select a boot device. If your hard drive is there, select that. Or, if you see one labeled 'Recovery' select that. If you select your hard drive and it boots, go to Disk Utility and run verify your disk. Then go to System Preferences and verify your drive is selected as the start up disk. If you select Recovery, choose Utilities from the menu bar and open Disk Utility. Verify and Repair your disk. Once that's done, try booting again. If those steps don't work, please provide a few more details, (like what OS you're running) and we'll move on from there.