Thermal paste conducts heat energy across the microscopic (air gap)surfaces of the processor and the heatsink. It is not water-based and should never dry out (but will eventually) when it does it loses its effectiveness. Don't use cheap paste that dries out relatively quickly.
Does that mean that the problem can be caused by the already dry pasta? a while ago remove the dissipators I cleaned the dry thermal paste they had and then connect the miner after restarting a couple of times started working at its normal power 2000ghs, however, I know that if I restart it is possible to return to the previous state Could it be the thermal paste that is generating this problem? Thanks for your comment!