Ohhh.... I did a thread on this problem in the Fall of 2007. I bought an H54L and just used it as a CD-ROM and a DVD-Video player for a couple months. Worked fine. But then it was time to get into Burning and I loaded the Nero 7 essentials from that disc that comes with the drive and lo and behold ...!!!.... afterwords, It would not play DVD-Videos anymore !! It would not even recognize the disc was inserted !!
I talked to techs and got no where. I finally got a guy at LG support that told me the Nero 7 ess. Install corrupted the Firmware (somehow, I don't know) and there was no firmware available for that drive at the time. He just swapped me out with an H55L which has worked perfectly ever since. (lol!) The Nero 7 ess. Install needs a 380 MB update after you Install it !!
First, get the "LG ODD Auto Firmware Update" program installed and double click the Icon in the Systray and it should show Ver. 1.06 is available and will ask you if you want to update and then do it. Make sure all other programs (including screen savers or anything that might Autorun are off) before you let the ODD update. This might restore the drive to normal. If your already at Firmware Ver. 1.06 then you'll want to re-flash. You need to get a 1.06 Flasher at the LG site. LG ODD Auto won't run if it sees you have the same Version it has.
I believe you can get the LG ODD Auto Updater at the same place where you can get the Flashers. I think its better to use it first; and only use the 1.06 Flasher if your already at Ver. 1.06 .
If this does not work then the drive is probably damaged. Call who ever you bought it from and get it replaced. If you don't feel comfortable with the Tech procedure above, then it might be best to just get it replaced under your warranty. The guy at LG told me ... not to install that nero 7 essentials with the H55L plugged in, again. And I haven't, and never will............