What happened to my laptop?

I have an HP G42-475DX laptop.
The other day I had my laptop plugged into my projector via HDMI.
I had the cord plugged in before I turned on the laptop, so it was NOT some kind of hot swap error.
It was working fine, and I logged into my windows, then the screen glithced... kinda like in this picture
http://i.ytimg.com/vi/Z6c8D9LLXVU/0.jpg

Then I shut it off, unplugged the HDMI and rebooted it.
This time the screen was black and the caps-lock button was just blinking off and on, and the fans didn't kick on full speed.

I try a couple more times with the same result.

I tried to remove and reinstall my R.A.M. (I've seen a lot of weird problems resulting from loose R.A.M.), then it turned on, but after the windows loading screen when it turns black it stayed black forever, and the caps lock was blinking.

I removed and reinstalled the R.A.M. again, but this time instead of booting into Windows I booted into my laptop's built in diagnostic tools.

While it was running the start up test the screen got pixelated, so I turned it off and back on, and the black screen caps blinking happened again.

The next day I turned it on and it worked perfectly.
Even the HDMI out works fine.
That was a week ago and I haven't had a problem since.

I'm wondering what it was, though, because if my laptop is about to die I'd like to sell it before it does.
But if not I'd like to keep it... it's pretty new still.
My friend says he thinks it was too humid in the room and that was causing problems with moisture.
If that's the case my laptop should be fine since no permanent damage resulted.
But it wasn't even that humid... which is why I'm not sure if that's what happened.

And I can't find any viruses or software problems on the laptop...

If anybody has any suggestions as to what caused that glitch let me know.
Thanks.