kobra:
If you are using the override system you can try first changing to the classic template. If you overlooked doing this and have not kept a log of your edits - You will have to determine the install date and most of the files will have this date.
It appears that you installed the column-grid module and you can begin there especially of you edited these files
I have been working back through this trying to find the cause, and couldn't, so I ran a fresh install of ZenCart without any customisations except for installing the columns module, and linked it to the old database. The same problem is there. In fact, when you try to change the formatting back to 'rows', it still stays as columns, even though when I check the sql database, it shows ROWS, but is not making the change.
The fact that the cart is a fresh install and the database is still the old one, makes me think the problem lies with the database. I have a test cart with test store front (version 1.3.7) installed and tested this mod, and it worked fine.
Any ideas?