I have 4890, samsung 22" monitor on DVI port and LG 32" LCD TV on HDMI port. U might need to set the TV on the right input channel (antenna, hdmi 1, hdmi 2, etc..) and also check the monitors in the control panel setting on your OS. Best thing is to connect another monitor and the TV at the same time, set the screens in control panel on the TV only, and after that just disconnect the monitor.
Read the manual of the LG manual for PC_mode on the digital interface. Your display is rated 120HZ for interpolating HDTV movies and TV shows. PC link must run on 60HZ scan only. Most HDTVS have pc mode settings on its digital interface(HDMI).
right click on desktop -> "screen resolution" and u should find your monitors here, using "identify monitors" u can see and choose the TV only. If u cant see the TV, than u are probably not connecting something properly, or the TV doesnt give signal.