fft – Effect of windowing on signals

I am having an input signal of frequency 1000Hz.Sampling frequency=16kHz.I am taking 128 input samples and then 128 point FFT was computed .Then the magnitude spectrum was plotted. I am not doing the normalization by 128.
So my two sided spectrum will be having magnitude of 64 on bin frequency 1000Hz.Now I found out power spectrum and two sided power spectrum will be having magnitude of 4096 on bin frequency 1000Hz.Now I take hanning window of length 128,multiply the input signal with hanning window and take 128 point FFT.Then when I plot the two sided spectrum,I am getting a value of 32 on frequency bin 1000Hz,16 on frequency bin 875Hz and 16 on 1125Hz.When I plotted power spectrum, I got 1024 on frequency bin 1000Hz,256 on frequency bin 875Hz and 256 on 1125Hz.I wanted to know how do we check the values that we get in the frequency domain after using windowing function is what we want