Plot[y/(32*[Pi]^4)*12^2*(2.09*10^-11)^2*100^2/(192 [Pi])
 NIntegrate[((x - 2*100^2)^2 - 4*100^4)/Sqrt[x]
 Sqrt[(x - 4*100^2) (x - 4*100^2)/
 x^2] (x^2 - 4*100^2*x +
  12*100^4)/((x - 5^2)^2 ((x - 100^2)^2 + (4.15*10^-3*100)^2))
 BesselK[1, Sqrt[x]/y], {x, 4*10^4, [Infinity]}], {y, 8*10^-3,
10^10}, PlotRange -> {{8*10^-3, 10^10}, {8*10^-44, 10^16}}]

NIntegrate::ncvb: NIntegrate failed to converge to prescribed accuracy after 9 recursive bisections in x near {x} = {5.57963*10^7}. NIntegrate obtained 2.5480460753667857`*^6 and 21453.774416999564` for the integral and error estimates.