I got an American model of LG. i can not tune it by auto nor manual can you please help
You can get a manual here: http://www.lg.com/us/tv-audio-video/televisions/LG-lcd-tv-32LG30.jsp . Click on the Support and then on the right hand side look for User's Manuals. Since the TV has a tuner for ATSC, NTSC, and Clear-QAM, the next question is what is your signal source? (analog, digital and unscrambled cable)
If you are using OTA, make sure that the input is set to Antenna. Use antennaweb.org or tvfool.com to check the direction to point your antenna and the appropriate antenna for your distance to the transmitter. antennaweb assumes an external antenna and is very conservative in the list of channels you should be able to receive. tvfool gives the stations available with different antennas. If you have several tvs connected to one source, you may need an amplifier in addition to the splitter. This also can help marginal signals come in since digital is either enough for the tuner to resolve or no signal. (Check splitters and amplifiers if you suddenly can't get a signal that you used to receive. Also check if the antenna has been turned.)
Menu > Channel > Auto Tuning or Manual Tuning. If Lock System is active, you will need the password. Auto Tuning only searches for digital or cable channels. The manual tuning option should provide the signal strength as well for digital stations (as well as letting you search for analog signals or all signals (digital, analog, cable).
Use the input Cable for coax cable connections. Other inputs will not allow you to search for channels since they are meant to be controlled by the set-top box feeding the system.
I hope this helps.