Refreshing a windows form

Hi, I am developing a project in C# windows application project. All of my forms peroforms a large number of data manipulation using oledb connection to oracle database. But when i start processing something and switch to other application like ie, sqlplus and then again comeback to this win form it not shows up until it finish the task, it was running.And in the user interface of the form it holds some parts of ie or sqlplus. i tried with this.refresh() but it does not work. Anyone have any idea how can i solve this problem. I have p4 and 512 MB ram so i dont think there is any problem with memory. Thanks.