[eluser]Burak Guzel[/eluser]
My first guess would be that your database might be overloaded. You have quite a bit of dynamically generated content on your front page. You probably would gain a big performance benefit by looking into caching, instead of running many database queries on every page load.
I haven't seen your code, so I can't really say what the problem is. However, it is highly unlikely that using CodeIgniter is the root of the problem.
