The constant (‘direct current’ or ‘d-c’ 0 Hz) offset is hiding the rest of your spectrum. This is a common problem, and since removing the constant offset does not affect the rest of your signal (and you can easily recover it if needed, since it is the mean of your signal), remove it before calculating the fft to see the rest of your spectrum.
This works:
[d,s] = xlsread('Good State.xls');
Time = d(:,1);
Good = d(:,2);
L = size(d,1); % Vector Length
Ts = mean(diff(Time)); % Sampling Interval (Assume ‘seconds’)
Fs = 1/Ts; % Sampling Frequency (Assume ‘Hz’)
Fn = Fs/2; % Nyquist Frequency (Assume ‘Hz’)
Good = Good - mean(Good); % Remove D-C (Constant) Offset
Y = fft(Good)/L; % Scaled Two-Sided Discrete Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector
Iv = 1:length(Fv); % Index Vector For Plot
figure(1)
plot(Fv, 2*abs(Y(Iv)))
grid
xlabel('Frequency')
ylabel('Magnitude')
