Nicolas,
I did both of what you suggested. The USPS issue still persists. I have attached a new screen shot. Despite what you are suggesting, we did NOT change anything on our end. We noticed this because people are making order, but not paying for them. I know only using PayPal they are required to do the extra step and pay via PayPal instead of on our site, but when repeated orders came in and no payment verification, we realized something was wrong.
As you saw in previous screen shot also, I *did* select UPS and PayPal. It says so on the screen. That was AFTER disabling USPS.
So I tried again, using my US address, I manually selected UPS and PayPal. In the second attached screen shot, you can see again, it is failing to even retrieve the UPS shipping quotes which I selected and basically, the order fails and never goes to PayPal. I'm assuming at this point, the reason you had success is because it was defaulting to your international address and by-passing USPS US and UPS?
Please let me know what is required for you to log in and examine this issue. Again, we have literally been ignoring the cart for about a year and just letting orders come in so none of this is due to any changes we have made. About all I do is update Joomla/HikaShop or plugins, none of which should have caused this... although we did just re-buy HikaShop business, and upgraded from free, but I don't see how this could have affected this???