Planet locked out of the S.G.C dialing computer. The world is believed to be the Aschen homeworld. It was the world where SG-1 originally encountered the advanced but hostile race, until the timeline was altered, preventing them from going there.
When the team later met the Aschen on a different world (the planet Volia), they determined that there is a one in four chance that P4C-970 -- the planet they were warned never to go to by the future Jack O'Neill -- is the Aschen homeworld.
HOME TO - Aschen
FIRST APPEARED - N/A
2010 - In an alternate future, Earth first accessed P4C-970 and, to their eventual detriment, encountered the Aschen. General Hammond orders P4C-970 locked out of the S.G.C. dialing computer after receiving a note of warning from the future.
2001 - SG-1 meets the Aschen on a different planet, and determines that there is a good chance that the planet they were warned about is the Aschen homeworld.