Exploding battery, now bootup freeze/crazy screen colors

Mid-2010 MBP (out of warranty), noticed that the laptop wasn't sitting straight and the trackpad buttons were hard to use, so I powered it off and took the back off to notice the battery had exploded, so I removed it and figured I'd just work with it connected to the power source in the meantime. Only problem is when I boot up, I am faced with this screen and it freezes, won't let me login (happens on both the laptop screen and Apple Cinema Display, so the ACD isn't as fault).

Anyone got any ideas on what it is likely to be? I've tried resetting PRAM etc. I have it booked it for the genius appointment on Saturday but just wondering if anyone had come across it before and how much repair costs would likely be on whatever parts may have failed (assuming it is hardware of course).

Thanks in advance!

Thanks for your replies guys. No idea how many cycles it had been through, but for the most part it was connected to the power source on the cinema display I'd say around 75% of the time. The battery definitely hadn't been through lots of cycles. No service battery message or heat issues, I do have iStat and monitor temperatures to ensure they are OK.

Took it into Apple genius who had confirmed GPU/logic board replacement, unfortunately not covered so it would cost $700 AU plus $200 AU for battery, then labour and taxes on top, over $1K all up so not worth it unfortunately. I will mention that it is a 17" MBP also, which is a shame they don't make them anymore!

Going to bite the bullet and look at an iMac as a replacement I think.. hopefully my 27" ACD with mini display port can plug into the second thunderbolt port to act as a second display.. I'd hate for both my MBP and ACD to be useless!