Need Help Please

I purchased the high-end theme. And had several problems getting it to work. A few things I figured out and fixed and it’s working. But when I opened it to customize it, I see the working panel to the left but I do not get anything in the preview screen but blank white. I’ve tried to increase the max_execution_time, that did not work. I tried to also deactivate plug-ins as suggested that didn’t work either. Also when I tried to upload the demo content it runs for a while and he gives me an error number 504. I am getting a little frustrated so I need some help, because I’m anxious to get this site up and running.