I'm trying to write a dvd movies (4.4gb) on a dvd (4.7gb) using nero 7 essentials.but every time it says could not locate start / stop points insert a blank dvd.what could be the problem?

Have you tried using another blank DVD? The one currently in your DVD writer might only be suitable as a drink coaster. Nero should have a check box that allows you to perform a test burn before the actual DVD is burned. It's not a bad idea to check that before you burn something for the first time.

You may also be able to check and see if the blank DVD is valid by simply inserting it into your disc drive and receiving a pop up that indicates options for this extra added disk drive. On Mac a disc should appear on the desktop. If neither one of these works, it may be that the disk drive itself is corrupted. I would suspect, in a situation like this that the disk drive would not be able to read the disc. It could be the actual file extension or type, but that is unlikely. If other DVDs, CDs, etc then there may be a problem with the connection. To troubleshoot try using the Control Panel and Hardware.