In the year 2000, a written note in Colonel Jack O'Neill's handwriting and with his blood on it emerged from Earth's Stargate reading: "Under no circumstances go to P4C-970. Colonel Jack O'Neill." Unbeknownst to the SGC, the note was sent from the year 2010 in an alternate timeline, one in which the Aschen covertly sterilized Earth's population. Major General George S. Hammond subsequently declared the planet off limits to Stargate Command, its address was locked out from the planetary database, and all contact with it was forbidden. (SG1: "2010")
Later, in the year 2001, SGC made contact with the Aschen through the Volians, which were a primitive farming society. Initially, an alliance was to be formed, but when it was discovered that the Aschen intended to devastate Earth with a biogenic weapon, causing sterility, concealed as an Anti-aging vaccine, the negotiations were dropped. The Aschen delegation immediately attempted to send a biological weapon to Earth through the Stargate, but the Iris was able to be closed in time to destroy it.
The ambassador of Earth had previously presented them with a "gift" of Stargate addresses, which would enable the Aschen to dial other gates than the ones remaining unaffected by stellar drift. However, the addresses contained dangerous and or useless worlds, one being a black hole and others the nature of which "gets progressively darker" as described by Jack O'Neill. (SG1: "2001")
By 2004, Aschen Prime was assumed destroyed by a black hole, likely the one near P3W-451, although it is not confirmed that they ever dialed the address, or if they did so, that they were not able to find a way to close the gate. (SG1: "Relativity")