I just download AU and the first day I got it I didn't restock anything, is there any setting or something wrong?
Well, it depends. I would need more information to know why it isn't working for me. What shop(s) are you refreshing at? How old is the account you are trying to auto buy with? What are the lists you are using to buy items with? What are your refresh rates?
The program will make a list for you. Click Actions > Manage Lists Then under "list to manage tab", find the shop you plan to AB in. When its selected, it will tell you if there are any items on the list. If not, click generate list (right hand side. Preset value to approx 10k) When its done, click on save changes (middle of program screen). This will save that list under the account.
Mine hasn't restocked anything for the last couple of days. It was working previously, maybe it's just the shops though.