Why is my systems Fan constantly ramping up?

So I bought this system at a thrift store a year or two back. played some games on it and then shelfed it a few months after i had taken apart cleaned it out from head to toe. washed its encloser and repasted the CPU and GPUand even cleared out the heat sink and PSU with extreme caustion so not to break any of the enternals.

and recently i wanted to play some older game titles so in to it off the shelf where it had been sitting for the last year or so. plugged it in then let it run the 4.90 update and now after i done used it to buy the games i wanted off the old PSN shop. it starts ramping up its cooler fan like crazy.

ive tried everything from cleaning the board to swapping the power supply and even reset the bios via removing the C-mos battery and holding down the power button for an hour. wich this did seem to work at first but the same problem has reared its ugly face once again and its stressing me out to my wits end. if any knows whats wrog with my system please help me im tired of trying and failing to fix this thing.