would this be a valid querry:

querry = "Select * From Transactions Where AccountName = ' " + accessName + " ' ";

When I hardcode the paramater in, my datagrid fills with the correct rows, but this way it just stays blank. How do I use a string variable as part of the querry string?

Yes, you can do that. In the debugger, what does it say the value of accessName is? You can all look at the SQLParameter class which will make your code safer from SQL Injection attacks if you allow user input anywhere.