How do I search all the values or names in multiple columns in one textbox?

0) Put the code into a try/catch block.

try
{
    con.Open();
    SqlDataAdapter comm = new SqlDataAdapter("SearchMain", con);
    comm.SelectCommand.CommandType = CommandType.StoredProcedure;
    comm.SelectCommand.Parameters.AddWithValue("@date", searchtbx.Text.Trim());
    comm.SelectCommand.Parameters.AddWithValue("@yearlvl", searchtbx.Text.Trim());
    comm.SelectCommand.Parameters.AddWithValue("@complaint", searchtbx.Text.Trim());
    comm.SelectCommand.Parameters.AddWithValue("@medicine", searchtbx.Text.Trim());
    comm.SelectCommand.Parameters.AddWithValue("@fname", searchtbx.Text.Trim());

    DataTable dt = new DataTable();
    dataGridView1.DataSource = dt;
    comm.Fill(dt);
    con.Close();
}
catch (Exception ex)
{
    // put a breakpoint on the curly brace above or below this comment
}

1) USE.THE.DEBUGGER.

2) If you use using statements, you don't have to worry about manually closing the conmection.

SqlConnection con;
SqlAdapter comm;
try
{
    using (con = new SqlConnection(conectionstring))
    {
        con.Open();
        using (comm = new SqlDataAdapter("SearchMain", con))
        {
            //...your code 
        }
    }
}
catch (Exception ex)
{
}

3) Your problem is probably going to be one of these (we don't know which because "has an error" sucks as as problem description:
    a) The connection to the database failed
    b) The stored proc wasn't found
    c) The parameter list is somehow incorrect.