No HDMI signal. I just purchased a LG HD TV (32LG10). I hooked up a Pansonic DVD upconverter using

Question

I just purchased a LG HD TV (32LG10). I hooked up a Pansonic DVD upconverter using an HDMI cable. The LG reflects no signal on the screen. I bought a new cable with the same results. I then hooked it up with the three cables (AV) and it works. I know the upconverter works right on an HDMI cable because I had just moved it from the living room to the master bedroom. Any suggestions? And is the picture quailty better with an HDMI cable?