Do you have the Platinum Hits version of Mass Effect? It's been a year since you asked this, but the topic is still open, so I'll give you the answer that worked for me. There is a bug with the Platinum Hits Bonus Disc version of the "Bring Down the Sky"
DLC that makes "Pinnacle Station" unplayable. You have to delete your system cache, then delete BOTH the "Bring Down the Sky" and "Pinnacle Station" DLC's. Then you run the Bonus Disc of Mass Effect Platinum Hits, and you should be told that an update is available.
This is the bug fix. After the update downloads, reinstall the "Bring Down the Sky" DLC from the disc, and then re-download the "Pinnacle Station" DLC. You should then have access to Pinnacle Station in game.
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.