Need to save Running Total and generate Weekly and Monthly Report based on date

Hello,
I have a sheet has a list of products, purchase amount (to be input by user), and Monthly/weekly running total:

Product Purchase Amt Running Total
POne 3 3

If I input 4 into Purchase Amt, Running Monthly Total updates to 7

Product Purchase Amt Running Total
POne 4 7

This continues for each product until the end of the week and/or end of the month is reached.
Once the end of week or end of month is reached, I want to save the Running Total for the week or month in
a Weekly and Monthly Report for each product for future reference Then I want the Running Total to reset f
or the following week and/or month.

Hello,
Thanks but this only generates a monthly report spreadsheet, but there is no running total on the Master Sheet anymore. Where did the totals comes from on Feb 2012 report? I am supposed to be able to enter a running totals on the Master sheet, once I reach the end of the month and change c4 to the first day of the beginning of the next month, all totals on the master sheet should update the Monthly Sheet. So February 2012 I will enter for the month all the purchases for each product. When I open on March 1st, it should have FEB 2012 populated with all the products and the total from the running total on February 29th should be the final total on the FEB 2012 sheet for each product.

Yes I did all that. When I opened the file the running total formula didn't work at all. The FEB 2012 worksheet was there, with values, not sure where they came from because the running total doesn't work. I thought maybe I needed to perform the test you stated and then it would work, but to no avail. Not sure why this isn't working for me, but thank you for the effort, I appreciate it.

Yep I understand how its supposed to work, it doesn't.