4th PS3 dies! :(

Today was another nightmare. I woke up in the morning switched on my ps3 to play some skate 2 and bam YLOD ( Yellow light of death ) i dont know what im doing wrong i always have my ps3 covered when its not in use its well ventilated and i clean it on a daily basis. I have terrible luck im giving up on the 60GB i requested a 80GB. Sad Sad day
I dont know why im having this amount of trouble with ps3's my ps1,ps2,psp all stillwork perfectly fine ( and they were all bought on launch day)