PS3 (Fat 80gb) False ylod?

[ExcelBoi]

Hey guys, so recently my ps3 (4.80 Dex Rebug) ylod'd so taking it apart and looking at the thermal paste i see it's very brittle and terrible so i buy me some Arctic silver 5 replace it put my ps3 back together boot it up and worked like a charm for about 2 weeks now yesterday i tried to turn it on and boom ylod again so I'm like wtf? Maybe I out to much thermal paste on so I flip my off/on switch in the back to turn it completely off i turn it back on and it boots right up and it's been doing this for 3 days so now im confused is it also my power supply? Because if i flip the switch in the back on and wait about 30 seconds no ylod or it will once and i do what I did before and no ylod im very confused and any tips would be appreciated thanks!