Here comes the fun part!
On a side note, Check whether your warranty is valid or not.
My old PS3 finally got sick and after almost 3 years my warranty from Target is still active!
The YLOD can be caused by over-heating. Or sometimes other errors or broken things.
But try this. I've known people that have done this and it actually worked.
REMEMBER, this can do damage on your system.
If you can tempory fix it, buy a new one and do a data transfer to the new one.
If you need a permanent fix, consider mailing it out to a shop specializing in repairs. They can diagnose the system and determine if it can be fixed through resoldering the video chip back to the system board with new solder balls. Some of the other community members recommend Endless Electronics.