Excel graph showing wrong data

I have plotted several months (Nov06-Oct07) of data and graphed it out. On my pc and several others, it opens correctly, but on several others, the dates start at 10/0/1900 and continue as 12/31/1903,12/31/1907, and so on. All the other dates start with 12/31 with different years. So instead of 1 year of data broken down monthly, I have 103 years of data broken down with 4 or 5 years  between. All pcs are running either office xp or 2003 with some of each working correctly and incorrectly. It appears that somehow the cells are being defaulted as time data instead of currency on a few pcs thus showing dates instead of currency ranges, and I don't know why.