If the little piece that Sam touched was a part of the Cube, then why didn't Sam received the informations in the first movie? He held it with in his hands a lot.
Just curious, but the insanity that Sam had, and the insanity that his grandfather had seem to be similar/the same... so what happened to his Grandfather? Touching Megs and touching the allspark fragment do the same thing or what?
The juice came out when he fell over in TF1 and it made the Mountain-Dew bot. This considered, am not sure why Sam doesn't have any effects from it then as it is so powerful. Maybe the fact that it is a shard changes the way it emits energy but there do seem to be some unanswered questions surrounding it.
In the ROTF book this is explained, He did infact have all the stuff in his head after he killed megatron in the First movie. It was all locked away untill his contact with the Shard activated all of it.
And why can only sam have these symbols? Isn't weird that robots need an organic to blow up the sun? I mean, Bumblebee held it a bunch, wouldn't he have the symbols?
Maybe because when Bumblebee was holding the AllSpark in the first film, it was still intact and therefore he had the choice of accessing its information or not. Whereas in Sam's case, he simply had a piece of the AllSpark, which was destroyed. Naturally, that things which aren't whole and, basically, "broken" in a sense, are liable to malfunction or give off spurts of energy like a power line detached from its conduit. In a Nutshell: Sam, and Sam alone, ended up seeing the symbols because the AllSpark sliver was reactivated, obviously from his touching it, allowing it to transfer its information to him during on its energy spurts.
Given that the AllSpark created the Transformers in this universe, I'm guessing that it when it wants, the AllSpark will allow Transformers to access the information it has within its memory banks. As to the how, again, touching it is probably all that needed to be done.