I second or third the blame the woman approach. I do recall reading a study somewhere that suggested that boner problems are cured/mitigated when the sex object becomes MORE attractive. This should be onvious.
If you're married and committed (kids, history, assets, life, respect, love, etc.) to a woman who no longer gets you ramped up and able to perform, you're in trouble. I sympathize. You're stuck with the crone. Do whatever is necessary.
Otherwise, get a newer, younger, hotter girl. Think its not possible? Read Rip's article on aesthetics and improve your diet, lose 15 pounds (I think you're fat) and your market value will raise. So may your dick.