Did you follow my suggestions? I don't think you did. Can you even code in C#?
I'll make it really easy for you:
1) Got to Yahoo! Finance by typing in your browser:
http://finance.yahoo.com
2) In the "Get Quotes" input box, enter the symbol of the stock you are interested in e.g. MSFT. Click on the button that says "GO".
3) You should now be presented with a page displaying information for Microsoft.
4) On the left you should see a column with links in it. Click on the link that says "Historical Prices"
5) You should now be presented with a page displaying historical price information for Microsoft. In addition, you should be shown a form to allow you to specify the date range and data to retrieve.
6) Enter the dates and data you want to download e.g. Start Date: Jan 01 2006, End Date: Nov 17 2006, Select the Daily data.
7) Click on the button that says "Get Prices"
8) The page should now reload and display the prices for the dates you selected.
9) At the bottom of the page there should be a link that says "Download to Spreadsheet". Copy the link URL to dissect it for your program e.g.:
http://ichart.finance.yahoo.com/table.csv?s=MSFT&a=00&b=01&c=2006&d=10&e=17&f=2006&g=d&ignore=.csv
As I said before, it's not rocket science. I'm going to make a wild assumption that you know what a URL is.
s=TICKER e.g. MSFT
a=BEGIN MONTH NUMBER -1 e.g. For January, use 0. For February, use 1
b=BEGIN MONTH DAY e.g. for Jan 01, use 01 here.
c=BEGIN YEAR e.g. 1989
d=END MONTH NUMBER -1 e.g. for November, use 10 etc.
e=END MONTH DAY e.g. for Nov 17, use 17.
f=END YEAR e.g. 2006
g=DATA TYPE, e.g. D for Daily, M for Monthly etc.
ignore=The format of the file to download e.g. CSV (comma separated values)
Are you with me so far?
To summarize:
1) In your C# program, construct a URL with the desired parameters to match your stock, date range and data type.
2) Connect to the url and read in the data response using the code I outlined in my earlier post.
3) Now you have to parse the data. Do you know what that means? It means splitting the data up into meaningful bits. You can achieve this by using .Split on each line that is read in to get the comma separated values.
You now have the raw data. What you do with it is up to you. If you want to display it, you can do. This is where your C# programming skills come in.