How to resize the main volume to its original or full size? I followed the instructions mentioned in one of the threads on this community to expand the Macintosh HD volume to its full volume. I rebooted with cmdR to Recovery Mode, opened Terminal, entered diskutil cs list and it said: "No Core storage logical volume found". What does that mean and how to get through? 

I need to merge the blank space of my HD with Macintosh HD and make it one. Screenshot is attached. 



Update:

The output from diskutil list is below.

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            189.0 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3


Output from sudo gpt -r show /dev/disk0:

start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  369140640      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  369550280    1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  370819816  605953319         
  976773135         32         Sec GPT table
  976773167          1         Sec GPT header


Output from sudo fdisk /dev/disk0:

Disk: /dev/disk0    geometry: 60801/255/63 [976773168 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: EE 1023 254  63 - 1023 254  63 [         1 -  976773167] &lt;Unknown ID&gt;
 2: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused
You are not required to use core storage unless you have a Fusion drive or need encryption. In your case, the drive does not have any core storage partitions. Your question does not contain enough information to determine what hidden partitions may exist on your drive. To determine this you would need to edit your question and add the output from the following commands.

diskutil list
sudo gpt -r show /dev/disk0
sudo fdisk /dev/disk0


You should enter these commands while booted normally to OS X. Some commands may ask for your login password. This is normal.

Assuming you just have a EFI partition closely preceding and a Recovery HD partition closely succeeding the Mackintosh HD partition, you can add the blank space to this partition by following these steps.


Boot normally to OS X.
Setup the Disk Utility application just as shown in your image.
Enter a new size of 1000 GB, then press the return key.
The size should change to the maximum value.
Click the Apply button. Note: This can take a while if there is a
hidden Recovery HD partition.