I have recently been out of the country and my computer wasn't used for about 3 months at all. I have a water cooling unit going into the CPU that I have just cleaned and refilled less than a year ago. When I start the computer after a few minutes it shuts off and after a closer inspection, I felt the CPU cooling block to be burning hot. The fan on top of the block is still working however could this be because of water evaporating somehow out of the H2O cooling unit or perhaps the filter isn't working any more?
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It could be coolant loss, or possible your seating isnt the same as well, or even the pump itself, but first whats your temps now vs then?