Adding column with primary key in existing table

To create a new column would be:
T-SQL SQL Server 2008 R2 will create something like this:

ALTER TABLE Product_Details
ADD Product_Detail_ID INT NOT NULL
--additional cells can be added if needed

CONSTRAINT [PK_Product_Detail_ID] PRIMARY KEY
--Followed by Clustered or non-clustered depending on need. in addition to
--additional indexing if needed

And it shounds like you already have a Primary key that you can remove with this:

ALTER TABLE Product_Details
DROP CONSTRAINT pk_Production_Details

You can right click on that table and click on "Script Table AS" and do
"ALTER" and it will give you a basis to work off of.

If you are doubting the effectiveness of that above transaction working you can test it by adding this BEFORE your CODE:

BEGIN TRAN

and to complete that transaction do highlight the following text and execute:

COMMIT

Or undo that transaction highlight the following text and execute:

ROLLBACK

That should give you some better understanding of how to work with what your needed to do and be more confident that the changes your making can be undone to some extent.

Hope that helps.