I suppose I should also mention that I am not ending my file names with .txt or .csv
If they don't have any file endings then when you go to open them windows asks you to select which program you want to open them with. If you open them with Excel then it immediately brings up a warning message claiming the data is corrupt or in the wrong format (or something like that). If you just click to continue through to opening the file then it still opens the file correctly and all the data is still fine ... I did this because with .txt at the end of the file was causing the file to be completely unreadable, even though it was correctly being recognised as a txt file in windows (also it was printing funnily over the serial as well).