Sum stops working after

Hi, i'm fairly inexperienced with using advanced formulae with excel.
I've been deemed the task to maintain our sales spreadsheet, however i've found that as i import more data, our Sum has stopped calculating when i do auto filters? I'm not talking about manually selecting cells and summing them up, i'm talking about determining how many rows there are containing selected infomation when i auto filter. (Eg: 57 of 2002 records found)
When i first imported some data, and right clicked down the bottom where it says Ready, and changed it to Sum, it worked fine, i've tried to do conditional sum changes, but i can't seem to make them work.
Now every time i get past about 40 records/entries, it the sum will say calculating, and then just simply say Ready.
I also have a differant spreadsheet, which has over 2000 records, which is still summing fine?
I've checked in options to make sure it is still saying Automatic, and cannot figure out what setting i need to change to allow it to sum larger amounts?
Any help would be greatly appreciated!

Originally Posted by Robvisionstream

Hi, i'm fairly inexperienced with using advanced formulae with excel.
I've been deemed the task to maintain our sales spreadsheet, however i've found that as i import more data, our Sum has stopped calculating when i do auto filters? I'm not talking about manually selecting cells and summing them up, i'm talking about determining how many rows there are containing selected infomation when i auto filter. (Eg: 57 of 2002 records found)
When i first imported some data, and right clicked down the bottom where it says Ready, and changed it to Sum, it worked fine, i've tried to do conditional sum changes, but i can't seem to make them work.
Now every time i get past about 40 records/entries, it the sum will say calculating, and then just simply say Ready.
I also have a differant spreadsheet, which has over 2000 records, which is still summing fine?
I've checked in options to make sure it is still saying Automatic, and cannot figure out what setting i need to change to allow it to sum larger amounts?
Any help would be greatly appreciated!

=SUBTOTAL(9,B:B)
will subtotal the filtered data in column B, check out subtotal in excels help file, or the function wizard
As for slow calculating, what does your formula look like