1) If I were in your situation, I'd disable the DVD Player in Device Manager and see if the errors persist. If they stop, I'd try removing, then reinstalling the ODD and re-enabling it. If the errors returned, I'd try testing the ODD in another computer before replacing it.
2) And since I've read of a lot of strange BIOS issues reported lately, I'd restore defaults settings to the BIOS to see if that changed behavior.
3) You certainly want to run an HDD diagnostic utility such as HDTune, or better yet, the disk manufacturer's proprietary diagnostic utility before concluding the HDD is defective.
4) You report the laptop restarted for no reason. Was this a "pull the plug" type of unexpected shutdown or slower, as in a BSOD? Does BlueScreenView from Nirsoft report any BSOD information if you run it?
5) You might also check out
http://rog.asus.com/forum/showthread.php?30418-G73jh-very-slow-and-freezing . In this case, what initially appears like a failing HDD, may actually be a failing power adapter. But in your case, don't eliminate the possibility of poor grounding either.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT