Mine got it when trying to install MGS4 onto my HDD, my guess would be harddrive failure
Your one can be fixed by just obtaining a security driver and replacing the thermal paste with a high quality paste like arctic silver. This fix has worked for a huge amount of people albeit it is only .3% of all PS3 owners. If you are a 60 or 20GB owner you may also want to change the paste for the emotion chip as well.
Power surge can be possible cause of YLOD.
Also if the inside of your ps3 is very dusty it can cause this as 1 guy had this happen to him and he took apart ps3 and clean out all dust in all areas and his ps3 is now working again from YLOD.
This is just some things to look at as they might help you on this YLOD problem... a YLOD fix guide is attached below