Hello,
I no longer have time to develop paint of persia, but I still have time to reply to messages!
It looks like a multi-screen problem like the previous message. The software keeps track of the position of the window, so if a second screen disappears, the window may be outside the remaining screen.You can try to put back the second screen (if it's the case) or delete the file that holds this info, but you'll lose other information stored in this file: C:\Users\yourUserName\AppData\Local\Paint Of Persia\User DataDefault\settings.json
BUT save yours files before and C:\Users\yourUserName\AppData\Local\Paint Of Persia\User Data\Default\settings.json if you have palettes or anything you want to keep in program settings...