ubuntu - My internal hard disk is corrupt and can't be accessed

I was fiddling around with Ubuntu. After restart, the boot menu disappeared. So I tried installing Ubuntu from a live USB.

This is what I get:

I actually had 3 partitions in windows - C, D & F which are now collapsed into one. So I tried "Try Ubuntu before installing" and started Ubuntu. To access the file system, I tried sudo fdisk -l which shows that I have a 1TB volume on /dev/sdb:

Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

So, I tried to mount it using sudo ntfsfix /dev/sdb. It shows the following output:

Mounting volume... NTFS signature is missing.
FAILED
Attempting to correct errors... NTFS signature is missing.
FAILED
Failed to startup volume: Invalid argument
NTFS signature is missing.
Trying the alternate boot sector
Unrecoverable error
Volume is corrupt. You should run chkdsk.

What do I do now to recover my files? Is the data still present in the disk? How do I recover it?

Update – I ran gparted, this is what I get:

.

Update 2 - I used TestDisk and obtained the following . But the size of My HDD is only 1TB what am I supposed to do next?

Answer

It looks like your partition table is missing. It may not be the only problem but let's hope for the best.

Use TestDisk to scan for missing partitions (like this). If it finds your old partitions then let it write the recovered partition table to the disk. It may or may not be enough to fully recover. It's hard to say what you did "fiddling around with Ubuntu"; e.g. you may have overwritten some data inside your partitions, I don't know.

In some cases, when you don't know what you're doing, reckless use of TestDisk may make the situation worse. It's a general good practice to make a clone of the HDD with dd (or ddrescue, especially if you suspect your disk to be faulty) beforehand; this requires time and additional diskspace though.

However if TestDisk finds your partitions exactly as they used to be, it should work without any issues, unless there are problems beyond the (missing) partition table.

If you manage to recover the partitions (i.e. they mount right, you can access all your files including your Windows system files) but the Windows doesn't boot, the reasonable thing to do is repairing the bootloader. I won't cover the subject here because you explicitly asked about recovering files only. Still you may ask a separate question if there's none yet that covers this subject – search first.

In a case your partition table recovery was unsuccessful or not enough to access the files, use the said TestDisk or PhotoRec (or similar tool) to recover (some of) your files to another disk.