Okay, a bit of simple biochem for you. Impotence is generally caused by only two factors; low testosterone and limited production of nitric oxide. NO is NOT nitrous oxide, but nitric. NO is a vasodilator, and the penis is vascular erectile tissue.
Drugs like Viagra, Levitra and Cialis work through this mechanism, but mostly through the effects on cyclic guanosine mono.phosphate. The body needs the amino acid L-arginine to produce NO (nitric oxide). NO cannot be stored. This pressents a problem for some. Using a supplement like arginine alpha ketogluterate will sustain blood levels of arginine.
Also of note, ATP, or adenosine triphosphate. ATP is actually created by the body from stores of phosphocreatine (creatine processed by the body for storage). That said, creatine "may" be of some help. ATP is available as a supplement, butt ONLY one has been proven (E. Rappaport) to survive passage through the gut. Peak ATP is the only ATP that remains bioavailable after ingestion.
On to testosterone- not too much really helps here. DHEA(dehydroepiandrosterone)is available as a supplement. It's a chemical precursor to test, metabolized into androstenedione by the liver. Cholesterol is also ,ONE step away from test, chemically speaking.
You can try all or some of these. Something WILL work, my friend.