New DVD read writer not functioning

sounds like the drive lock is not seating properly, (gearing mismatch)  

The drive tray lock is a peg on a round gear which locks into a groove on the underside of the tray (you can see it on the underside on the tray, 

at some point this gear has "slipped" and now does not meet this groove and closes before hitting this groove,   some manual manipulation of the drive tray can solve this but it is tricky

The easiest way is to "pop" the latch,  which allows you to remove the drive tray completely This "latch" is usually a sprung toungue of plastic which normally prevents the removal of the tray,  if this toungue is lifted the tray can continue on the gear train and can be completely removed, (the eject function will roll the gears forwards and backwards without the tray).

all you do then is to press eject (the mechanism gears will roll out) then you just insert the tray at the correct point (usually at full extend) to re-allign the tray lock (sometimes it takes a couple of attempts to get this right)