@Lucas provides good advice here as corrplot is quite useful for visualizing correlation matrices. However, it doesn't address the original issue of plotting a large correlation matrix. In fact, corrplot will also fail when trying to visualize this large of a correlation matrix. For a simple solution, you might want to consider reducing the number of variables. That is, I would suggest looking at the correlation between a subset of variables that you know are important for your problem. Trying to understand the correlation structure of that many variables will be a difficult task (even if you can visualize it)!
