I changed internally the drives in my 740 with a Liteon 1635 (older model with fast Forward) and a Liteon 20h4p in my 760 (no fast-forward on DVDrs and commercial DVDs, works fine with DVDrws). I had to dismantle the front display and trim the metal back plate of the front display to allow PC drives to fit.
Your Toshiba burner might not be compatible in the 740. When setting a new burner in a Liteon-based HDD recorder, the jumper needs to be set on Master. When the recorder goes into the “Hello” mode and doesn’t come out of it, it’s because it’s not recognizing either the drive or hardrive, that happens when no jumper is set or on slave, a bad cable, bad connection or incompatible and/or dead drives. In your case, I would first set the jumper on Master on the Toshiba and try to boot up again.
If that doesn’t work, I would suggest that you look at the sticky threads on this forum about replacement drives in the 5005, you find one of those drives and will work as described on that thread in the 740/760. One tip on one of the more recent Sony drive 190. I personally tried the Sony 190 which works fine in other older Liteon recorders but not the 740/760. I’ve tried Liteon 1693, 160, 165, 20A1P, 20h4p, Sony 120, they’re all compatible with the older ones with FF and the newer ones no FF.
When I dismantled my front displays, I took the opportunity to take the small ON/OFF, EJECT board off and pry the blue/red LED light off the board and reinstall (2 minutes when everything is dismantled) now I don’t have “laser pointers” in my living room anymore !!!
Good luck, let us know about your progress.