the review step is not loaded when I access my one step checkout. I'm getting the error saying that there are no payment methods available, but when I'm logged in it works perfectly. How can I load the review regardless of whether the payment method is loaded or not, or the user is not logged in. - Magento 1.9
With review step you mean the last step in the checkout process?
I think that you are having some setting in your system configuration that restricts payment methods to certain customer groups. When a customer is not logged in, it has the customer group "NOT LOGGED IN - ID: 0) by default. My guess is that you have a wrong setting somewhere in system > configuration under payment methods or onestepcheckout.
The order review is the last step in a checkout flow which contains a summary of the steps before which is your order. If you want to get there without payment method, you're going to have to do some tricks which I do recommend in particular. What is the reason you want to skip this?
The payment method has important settings for an order like taxes, country availability and more. Going without will be a tough job, what I would recommend is set the most basic payment method by default and try to hide it. The "checkmo" (Check Money order) payment method is a default one which is suitable for that but you will have to add some logic to select it automatically and hide it if you want.
Checkmo is commonly (mis)used as a way to allow something like "pay in store". They just change the name/title of the payment method and customers will pay in the store, it has no restrictions. It is for that reason also oftenly used by developers to get around payment stuff. I would recommend to take a look at that. (System > Configuration > [Sales] Payment methods?...)
Alternatively, there are a lot of extension available that allow you to limit payment methods to customer details like a customer group. They could be useful (I can send you one from my private collection if needed, have to search for it though)
But going without a payment method will be challenging. The payment method is basically the last link that can make an order happen or not. If you get past the payment method, you will get an active "Checkout" button and an order can go through. If you still want that, please explain me your use case a little more in depth. Like what do you want to accomplish? There's most likely a better solution.