Panic kernel problem

I just bought a second hand imac off ebay (late 2009 model. The 21.5") and I'm having a bit of trouble.
The first time I started it, the kernel panic screen came up. I turned it off and then back on two more times and the same thing happened. So, I started it in safe mode and checked all the files with file utility and it found no problems. I also connected to the internet and updated all the OS X updates.
It seemed to be running okay, so I turned it off and restarted it like normal and that was fine.
But when I turned it on this morning it had another kernel panic. I turned it off and tried to restart it in safe mode but I just got the kernel panic page again, then it popped up with a message saying the computer had to restart because of a problem but it just restarted back in kernel panic again and then it popped up with the message saying it had to restart. It just kept doing this (4 times) before I turned the computer off.
Do you have any ideas?
I contacted the seller and they said it had never happened before.

 

The seller had just installed some new ram so I took one of them out and its working perfectly now. Thanks for the help though.