Excel Hiding/Deleting Rows of Data?? (HELP)

I've been working on the same CSV file in Excel for a couple months.

It has 12 columns (with headers) and about 650k rows of data.

All of the sudden, I have noticed that cell A1 is replaced with what appears to be a random value from one of the text fields instead of it being the header test. Furthermore, thousands of rows are not showing and there are no blanks in their place.

I spent today looking into it and found that if a row of data starts with a dash, it causes problems and the data above it is hidden. I say that it is hidden because I can see all of the rows if it open the CSV in Notepad++ but if I open the same file in Excel, I do not see it.

I used Find & Replace in Notepad++ to replace all fields that start with a dash and then the file opens fine in Excel.

Why did this just start happening? Those particular fields have not changed the entire time I have been working on this file.

I'm using the same computer and no Windows (7 Pro x64), Office (2010 Pro x32), or Add-In updates have been made.

Thanks.

Steve

Any suggestions?