Plot power spectrum from FFT

Hi,

I want to plot power spectrum using FFT. I use the below code but I didn't get the spectrum and instead I got the below graph.

Please advise where my code is wrong. Thanks

x = xlsread('testcode.xlsx');  fs = 100; x = x';
y = fft(x); 
n = length(x);          % number of samples
f = (0:n-1)*(fs/n);     % frequency range
power = abs(y).^2/n;    % power of the DFT
plot(f,power)
xlabel('Frequency')
ylabel('Power')