Problem Adding New Clients

Any advice would be greatly appreciated as this is really starting to drive me insane! Especially when I have a customer waiting in front of me.

Basically what is happening is when I'm adding new clients, after pressing the +, it's a good 45secs before I can enter any name or any details in any fields. After I have entered the name and tab down to the next fields it freezes and thinks again, for another 45secs. After a good minute and a half can I finally enter more details then just a name. The computer is whirring of its head at the same time.

Installed onto Macbook Pro with the backup of all my clients and info, go to add a new client there and same thing, computer starts whirring, fans going crazy takes for EVER just to enter in the basic details for a client, that no address just name, phone and email and it takes forever.

Any ideas anyone, does billable have a limit to the amount of clients it can process, I have around a 1000 or more, seems like the only reason for it. Will profit train fix or will I have same problems? I need to do something about this sooner or later as its causing havoc every time I have a customer and a little bit of pressure.