When I try to log on it says "Do I want to leave my current game?"
Now that thats semi fixed let me try and help. I have not ever got that error but it might have something to do with your PS3, or your disk/download. If you don't give us more information it could be numerous things...
when i try to log on it say's do i whant to leav my current game
Some ideas on what more information is needed to address your issue:
Which version of Starhawk are you using? Disc, Downloaded Multiplayer Edition, Downloaded Full Game, etc.
Is your PS3 running the current version of firmware? Current version: 4.31
Is your PS3 connected to the network (PSN) and is it connected via Wireless or wired?
What is your connection speed? Visit www.speedtest.net on your computer and post the results here (the connection test on the PS3 is never an accurate representation of your actual speed).
If you are using the disc version, have you redeemed the Online Pass code that should have been included in the packaging? If you bought it used, have you bought an online pass from the PSN Store?
Does the error happen with any other online games?