I am way too familiar with what you have just posted. The ylod has a laundry list of trouble shooting. It sounds like you covered about 5 of them. If the fan is blowing extra hard, then this a cured "at" orsShortly before your ylod, it was postponing the fail, there is no thermistor sensor on these fans. They basiclly run at alittle under 12 volts. ( 1 of Xbox's issue was they only have 5v going to each 12v fan) ie: heat equals failure.
When you are temporarily not getting the ylod when holding down the eject button you are temporarily postponing what would be the systems initial power up sequence. At this point you will most likely have to search for schematics and you a multimeter to trouble shoot. Good LUCK
I have also had systems that sounded like a jet taking off , and it is still playing to this day 6 years later.