My LG RH177 does not read and write DVD-R anymore. DVD+R disks work well at the moment. Any idea? Thank you.

Hi,
There are three things you can do that will eventually give you a working solution. Depending on the level of problem. Start with 1 progress to 3 until it works.
1. Use a cleaning disc. (one that use an alcohol based liquid)
2. If the cleaning disc does not solve it, you can use an ear bud, with some iso-propyl alcohol to clean the DVD lens on the drive directly. (you have to open the player and the drive)
3. The guaranteed working solution is to replace the DVD drive inside the player. This is quite a simple process, as most players use a standard IDE DVD-ROM or DVD writer.
You simply remove the face plate, (apply power to the drive, and press eject first) the tray will open. Unclip the tray face, and then with the tray open you can unclip the plastic face plate too.
Remove the old drive, and fit the new drive by reversing the removal procedure.
Once everything is assembled you should be able to watch DVD's again. If you can't find a cheap DVD drive locally, try ebay.
I have done this on over 50 players for my clients in the past. I use LG DVD roms and DVD writers for the DVD recorders, irrespective of brand.
Let me know how it goes.