Excel slow to respond..

Hi,

I have a workbook which has 4 worksheet linked to the main worksheet,Basically a data entry book which we used to update regularly by saving
as changing the date and creating a new book from the old one..suppose we need to update today's status we usually go to 6th book and save as
to the 7th and make the changes,such is the process so when we are making the 9th or 10th workbook those books are very slow to load,respond and taking ages to move the cursor from cell to cell.we used to copy paste values in the sheet..if your trying to copy paste on 9th or 10th book
it will take at least 3-4 mts to paste..because of this I've a make a new sheet after 3-4 days and copy all those formats and formula's from the
old sheets.im using office 2007 and i'm having validation lists,a macro(IS ERROR)..

Any Suggestions Please..

Thanks,
Ak