Changing horizontal data to vertical

I have a problem that I'm not sure transpose can fix.

I have a database aligned horizontally. It covers 25 items, and then 40 sub-categories of each item. So, every 40 columns, everything starts over with data for the next item. So columns 1-40 cover item 1, columns 41-80 cover item 2, ... through all the items. I want to change it to a vertical format where the subcategories lineup. So if there are 10 rows that track the sub-categories over time, I'd like the data for ITEM 2 in rows 1-10 of columns 41-80 to be placed in rows 11-20 of columns 1-40 (under ITEM 1 in rows 1-10 of columns 1-40), and ITEM 3 data in rows 1-10 of columns 81-120 to go into rows 21-30 of columns 1-40, etc. through all 25 items.

1 item = 40 columns and 10 rows.
Goal is to get it to where instead of them being laid out side-by-side horizontally, they are rather one-on-top-of-the-other vertically.

Rows 1-10 are dates, and the 40 columns are data points I'm looking at for each item. The horizontal layout gives me data by date. I need to have the data organized vertically by the data points (the 40 columns) to run regression analysis in another program.

I'd like not to do it through grunt work and I think it would be helpful to learn how to do this. Any ideas?