Help! Macbook asking for PO's password?

I can't log in! I've been having a kernel panic issue on my older white Macbook, 10.7 Lion. It has been repeatedly giving me a 'you need to restart your computer message'. I have uninstalled the only recent things I had put on my computer, which were Wine and Winebottler, attempting to run Irfanview on this machine. I've given up on that for now, and don't know if it's caused this problem, but more immediately, It has somehow resorted to the previous owner's password request at startup. I changed all this when I bought the computer (a couple of years ago from a responsible seller), but where do I go now? I was following an Apple troubleshooting guilde for resetting the PRAM and this is what happened after pressing command/option/P/R at startup.

Thanks