I installed two different Demos from steam and neither one will play!

If you're trying to get the demo ticket for the contest, I recommend VVVVVV. ;P

I'm not. I was trying to play Dungeons and Dungeon Siege 3

You don't miss anything with Dungeons... and as far as I heard, DS3 unfotunately as well :(

I think it will go better as soon the summer sale is off again.

I read DS3's article in GI and wanted to check it out. And none of the other demos suited me, and I am NOT waiting 15 hours to play Witcher EE

Oh my god, I was so disappointed with dungeons. I mean, I guess it's an ok game on its own, but you cannot help but compare it to Dungeon Keeper...

Yeah i am the same i so wanted to like the game but i just cant play it without going Dungeon keeper does this better.

Apparently TF2 counts as a demo. I guess they're just checking to see if it's a game with a free price listing.

What does mean they don't play? When you click play then nothing happens or what?
Have you verified the game integrity?

They don't play. I tried Dungeons and Dungeon Siege III

Again, what does it mean? When you click "Play" what happens? Nothing, does the Steam prepares game to launch and then nothing happens, or does it crash during loading?
Have you tried to verify integrity of game files?

DS3 Crashes and Dungeons just gives me a black screen with music

... That sounds to me like your computer simply can't run those games. Less a Steam issue, more a hardware / driver issue.

Why ask here instead of the Steam forums?

I also ask myself why people here talk about steam and not on the steam forums ??
I do not want to hear about this ultimate DRM scam here....