Thanks for the feedback and yes in hindsight my question was too generic.
I had created a report bringing in data from various sources for some reason when I went to refresh the data is was just spooling and taking a really long time. When I looked at the source data one of the tables suddenly had a lot of Columns with null values added. Read a lot about unpivoting the data and removing blank rows etc etc. Long story short was too close the data and after sleeping on it just realised i had already unpivoted this data and just needed to go up to an earlier step and remove the blank rows.