Hi Sylvie, What brand is your external hard drive? There might be some compatibility issues with the macOS High Sierra. And if not so then, your external hard drive file system seems to have become corrupt hence there is no recognizable structure on your drive. Your data is still present on the external hard drive, but due to the corruption of the structure, you won't be able to access it. Please be cautious - don't format your external hard drive until unless you have extracted your data from it. After data restoration, you can navigate to the Disk Utility and select your hard drive for initializing. On your macOS High Sierra, you can format the external hard drive to APFS, HFS, HFS+ however if you plan to use your external hard drive as a Time Machine then let it be HFS or HFS+. Here is a guide which might help you recover your data https://www.stellarinfo.com/support/kb/i...-data-from-initialized-mac-har-drive Helpful read...

Hi, you can still run Disk Utility's First Aid on your unmounted drive. To do so, select your drive from the Disk Utility left corner and press First-Aid. Wait for the process completion and the Disk utility will let you know if your drive needs repair or formatting. P.S. backup your data and then erase the drive with MacOS Journaled.

Seems the SMC & PRAM & HDD is fine, there might be some problem with your Logic Board. Try to run Apple Hardware test. Follow the below steps to run Apple Hardware Test (AHT): You need to disconnect all external devices connected to Mac before running Apple Hardware Test. (1) Place the Mac on Hard or ventilated surface to avoid any kind of error (2) Restart The Mac and Press & Hold the D key on your keyboard (3) Apple Diagnostics starts automatically (4) Select the language you want to use & click the right arrow (5) Click the test button to start testing, press T (6) Review your test results after completion (7) Again restart the system to quit Apple Hardware Test

If you get booted successfully to Mac OS X Utilities using Command + R then you have the chances to restore your Mac either to your last OS or Time backup. Otherwise, get a working bootable USB and re-install macOS afresh. Later, restore your data from Time Machine.

Try Stellar Phoenix Mac Data Recovery Bootable CD to boot your Mac and salvage the data. Once done, you can replace the HDD and restore data from Time Machine and Stellar.

You can give a shot to Stellar Phoenix Mac Data Recovery https://www.stellarinfo.com/data-recovery-mac.php software to scan your hard drive and locate all the deleted Office for Mac files. Hope you stopped copying any new data to the hard drive. You surely don't want to overwrite the existing deleted file information. By the way, you should have backed up your macOS with Time Machine. It's a complete free in-built Mac utility and there is no reason as to why you do not have the Time Machine backup on your Mac. Anyways, if some of your important PPT and MS Excel file gets deleted, and that is too from Trash folder, then you need to use a above mentioned data recovery app. I recommend you change the preference to only Document in your Mac system, so that this recovery software scans only .XLSX, .PPTX and .DOCX related files only. It will exclude all other file formats like JPEG, OPNG, GIF, MP4 etc. and takes less time in scanning.

Hard drive replacement will not be a great deal since there are readily available guides that can help you perform a safe replacement. However, your Time Machine data (troubled Time Machine actually) sounds to be of great concern. You mentioned: “I connected my Time Machine external hard drive to MBP, it didn’t worked properly. Tired with another Mac but no luck..” What exactly happened to the Time Machine disk? Were you able to perform a Disk Utility Verify / Repair on separate macOS Yosemite 10.10 and below versions? If you are running macOS 10.11 or 10.12 then you can only repair (not verify) the Time Machine external hard drive. Also, let know if your Time Machine external hard drive have components failed already or about to get failed. You can monitor your hard drive if the media is producing a strange sound such as clicking noise, buzzing, ticking likewise. Unable to Mount the Time Machine (as it appears in the Disk Utility) You can download a data recovery software that supports Time Machine data...

The primary goal should be to extract all data from the hard drive that has been erased/formatted / deleted (but not wiped)**. But to do that you require a booting macOS. Unfortunately, when a hard drive is formatted or deleted entirely (removing macOS itself), the Mac hardware will only become a showpiece. You cannot make it run since you lack an original DVD or a bootable USB to start the Mac. As said above, data recovery becomes a primary object before you reinstall macOS. Bootable data recovery is possible with a file recovery program that provides a bootable DMG file of macOS with the copy of the software. Once this bootable DMG is acquired and made into a booting USB drive, you can start your Mac and select the bootable drive (using Option key) to select boot disk. The data recovery through boot disk targets the Macintosh HD (which now acts a seconday drive) and perform recovery of files. Once data is all recovered and safely exported to another media you can create another bootable macOS USB and...

If you have emptied the Trash folder of Mac, then there is very less probability of data recovery using the OS X itself. Terminal will be of no help to recover deleted files using command lines. However, still you can recover your deleted files. First Method: Restore data from Time Machine Backup If you have previously setup Time Machine backup, then all your files and folder are stored on the Time Machine. In addition, data restoration from Time Machine is quite and you can take the help from this article to restore your deleted data back. Second Method: Use a Mac data recovery program: Data recovery software can help you to recover deleted Trash data back within minutes. They uses advanced file recovery algorithms and provide immediate recovery to data-loss. I personally recommend you to download and install Stellar Phoenix Mac Data Recovery utility for deleted file recovery. The software is also capable of recovering deleted files from Time Machine, BootCamp and Password Protected Hard Drives. Future...

I second Sam Freeman replies. A Mac will boot up and show you a message like "Your startup disk is almost full" but it won't refuse to boot. Your disk seems to have developed some issues. Is it acting straneg like clicking, ticking sound etc.? More importantly, do you have a backup of your Mac hard drive? If backup exist then you can restore your Mac from Mac OS X Utilities and copy your data from the backup. Erasing the MBP drive will eradicate the file system problems. However, it will not work on a physically damaged hard drive. FSCK - Restart your Mac and press-hold Command+S button while Mac is booting. You’ll enter single-user mode, which will provide you with a text-mode terminal. Type the following command into the terminal and press Enter to start a file system check: /sbin/fsck -fy The command will run through several phases of checks. When it’s done, you’ll see a message saying “** The volume [name] appears to be OK” if everything is fine. If it found problems, you’ll see a “***** FILE SYSTEM...