I have a john deere hydro 165 The engine dies when I engage the mower blades. I have cleaned the deck and the beltsnare all on it seems that it doesn't have the power

Check your safety switches. If this is a newer model then it may have a reverse switch that is sticking and wont allow it to run with the blades engaged in reverse.

I agree with cdad, sounds like a safety interlock someplace... however, can you clarify, when you said it seems like it doesn't have the power... does it simply shut off, or does it sound like it stalls out?

Hi,
Sound like the seat switch, if the deck/blades will turn freely without the engine running. Some of this model would operate if you simply unplugged the connector. It is easy enough to test even if it is not one of those by jumpering the wires on that model. Note that I am advising against running it without a working seat switch, just saying how to check it. In a very few cases I have seen a bad electric PTO switch do it since there is also a second circuit in it.
Peace,
Clarke