By mistake, my matshita uj-8505 was changed to region 3. How to change the dvd region back to 0?
I don't believe there is a region 0. DVD regions are numbered 1 through 8. Anyway, open up Device Manager, expand the DVD/CD-ROM arrow and double click your drive. Select the DVD Region tab and pick your country from the list. Keep in mind that the number of changes you make is limited. When you're out of changes the drive will be locked. The number of changes left is shown in the dialog.