Had a similar problem myself. PC in hdmi out to Marantz recieve then back to a samsung lcd TV. It is a matter of luck if you ask me. Tried everything you guys mention, and nothing was 100%. For several weeks, no problem with switching back and force, then all of a sudden the TV says no signal. Switching hdmi ports made no difference. After months of toying with this, i found you can try the following: With everything turned on, unplug your PC monitor. The TV should pop back on. Then plug your monitor back in. THen hopefully both will stay on as extended desk top. You may have to repeat this 3 to 4 times before both will stay on. Usually, the PC mon pops back on and the TV is no signal. 2nd method: unplug your tv, not just turn off, but unplug the thing, wait ten minutes. Then replug and start over. So far these two method has worked for me. And yes, i can't explain it. But it consistant work for me. I have learned not to question it.
Also, i find this problem less likely to occur with a newer TV, my new samsung works a lot better than my older philips.