I think this is very basic engineering solution that your are trying .
Read this all link as I found this to be very helpful to understand basic functionality of LinQ .
Apart from this I would like to give solution for your issue not in the form of code but in the form of algorithm.
1) Connect the database
2) Use that connection to run LinQ Query
3) Declare one variable which will store YES/NO for result
4) Write SELECT query to find out the data in table If exists query will return YES otherwise NO
5) Make use of this condition to process further request.
Hope this helps , If yes then plz accept and vote the answer. Any queries / questions on this are always welcome.
Thanks & Regards