OS X :: MBP Monitor Not Working

I have already read other threads that are similar... but not the same as this.

I have a 15" late 2007 MBP that has always worked great, until recently. (10.5.8) The screen was blank this morning. I closed the lid, but the computer did not enter sleep. I opened the lid, and still nothing. (I can still hear the fan working)

I held down the power key for 5 seconds and forced the computer to turn off, and then rebooted. The computer started up as per normal, but still no screen activity. I plugged into my TV - no output signal.

I close the lid again to attempt to sleep, but no sleep. The computer is still running, even with the lid closed. I open the lid, still the same.

After doing a bunch of different things over and over, the screen came back on!

I came back to the laptop later in the morning, and I had to spend 1/2 an hour repeating the above process all over again. There seems to be no logic in my process that gets the monitor working again.

Does anyone think this is a monitor problem, or possibly a latch problem? I've heard that the latch is an important part of the monitor...

(I did upgrade my hard drive myself about 6 months ago, but no problems since... until now.)