Q:

How to decrypt a MD5 hash

I have used the following function to encrypt my password:
HashPasswordForStoringInConfigFile(Password, "MD5")

Now I want to decrypt the password again. 
Note I'm showing the encrypted password in a grid-view and I want to decrypt it when the particular row goes in edit mode. 

A:

The simple answer is "you can't"
The idea of hashing is to generate a "safe" code from the real password, where that code can be stored in clear text; in a database (or text file) somewhere where other users might be seeing it somehow.  
When someone tries to login, your system would compute another hash from the new login and then compare with the existing hash from your existing database, if the hash matches, then you know it's the correct password and then you can allow them to login, otherwise, it's not the same password / login-failed. 
The reason why you cannot reverse the hash is because a hash is computed by doing the following steps:
1) Taking the password into some algorithm to:
2) Generate a very large string, then:
3) Chop that string and:
4) Take a part of it as your "hash"
So you see, even if you are superman in decoding and can figure the algorithm out, and know the hash code, and managed to reverse it back into the original form, then you would still have parts of the password missing, hence unsuccessful. 
This is why Hashes are secure.  
I hope this explains it.