What steps did you take to add Seti@home?
After you start Boinc, you should have the simple view of the Boinc manager.
At the lower portion of the display, there should be a portion that says Projects:
Click the add project button. That should cause a new window to appear. If it's not already clicked on, click the add project then the next button. New window, scroll down and click on seti@home and click next and follow the commands on the next few pages. You will need to sign up with the account your created. If all goes as it should, then the project will be added and it will begin to download some work units. The estimated time are going to look very long, but after you have done some 20 work units, the times will come down as it gets a better idea of how quickly your computer completes a work unit.
Mert, I've looked at your computer and it is attached and has downloaded both CPU and GPU work units so looks like it did add the project. Now it's a wait and see how it processes the data. If you have any other questions, just let us know.