I found TestDisk tool to recover the lost partition. Following are steps I performed to get my lost partition recovered.
I started TestDisk with admin rights (Select the .exe and right click and select "Run As Administrator". You will see similar screen:
Then press Enter to proceed to next step as shown below:
Select your hard drive that has lost partition (I choose the highlighted one because of 500GB) and then press Enter to proceed to next step as shown below:

When you are on above screen, you can perform "Quick Search" to find out all partitions for selected Hard Disk. Select [Quick Search] option using arrow key and hit Enter. Below screen shows all partitions.
Use left/right arrow keys to see the partitions.
* = Primary bootable,
P = Primary,
L = Logical,
E = Extended,
D = Deleted
Select Primary partition and press "P" to list all files in that partition. You can verify your partition using lost files.
Once you are sure that you have selected the correct partition, you can press "q" to go to previous screen.
When you got back to previous screen, then press Enter to proceed to next step. You will get similar screen shown below:
When you are on above screen, select [Write] option and hit Enter, and press y to confirm. Once it is done, TestDisk will ask you to restart. Quit the TestDisk app using [ Back ] option and exit.
Leave your hard disk connected and restart your machine. After restart you will be able to see your hard disk. It worked for me and thats why I am blogging it to help others.
Below is the step by step guid.
http://www.cgsecurity.org/wiki/TestDisk_Step_By_Step
Thanks a lot TestDisk...for saving my money and DISK as well.