My cart worked PERFECTLY last week and now nothing!

I had changed from the standard green template to Cold Steel (changed back) and that wasn't the issue.

When I'm going through the checkout process, I can get to PayPal, fill out the information and then hit their "submit" button. At which time, I'm returned to Step 2 of the checkout on my cart. The money is not coming out of my personal PayPal account nor is it going into my business PayPal account.

I'm not sure where to look for the error.

And I am using the most current version of Zen Cart.