Rising (1) - S1-E1
Continuity mistake: When they first arrive on Teyla's planet, the DHD is close to the gate. When the wraith attack, the DHD is much further from the gate.
Continuity mistake: Right at the end, after the entity has gone through the gate, we get an overhead shot of McKay lying on the ground in front of the gate. His legs are stretched out straight. In the next shot, one of his legs is bent. He's unconscious, so he shouldn't have moved.
Revealing mistake: Steve (Wraith)'s belly appears not to match the rest of the Wraith character's skin tone. Clearly, it is a human body rather than an alien. (00:31:36)
Answer: Because even all 4 Naquadah generators (one was destroyed) together is only enough to dial Earth for approximately 1.2 seconds (As seen in the episode "Letter from Pegasus"). Further, if Earth had found a ZPM, they would dial Atlantis and let them know. After all, the SGC has no other use for a ZPM than to dial Atlantis.
Grumpy Scot