What is a problem can you tell me ?
It can be a myriad of problems. First of all you tell us the specs of your PC by going to Computer-System Properties if you use Windows or if you use Linux go to Applications-System Tools-System settings. Low performance PC may not support latest version of Multibit HD, even latest version of Multibit Classic is quite heavy.
We don't know where you downloaded it, always download from official website , Multibit.org and not other places as you risk downloading from other places.
Check if you have the latest of Java installed as Multibit is written in Java. If you have Linux you have to go through some steps, I will tell them for you if you confirm that have Linux.