If you have ever done a random response analysis you'd know there are a lot of steps. On top of that you know there are a ton of pit falls such as not defining the correct frequency response range, or units, or output set request to ensure the file size isn't 100GB large. In this image, which is attached for download, you may find what I've found to be very helpful in performing random response analysis.

Work from left to right you'll note the inputs. First with normal modes analysis, followed by frequency response, and then random response; which follows the golden rule of PSD frequency range times 3 : 1.5 : 1 for the respective analysis. For example, if the PSD is up to 500hz, then the FR analysis should go up to 1500hz and the normal modes up to 3000hz.

For more I'd recommend looking at our virtual online training (OptiStruct for Dynamics Analysis), documentation and tutorials.