Erectile dysfunction is not related to vitamins despite the fact that many websites selling vitamins would have you believe otherwise. If your body is vitamin deficient in some way this may have an indirect effect on sexual function but other symptoms would also be seen.
There are a number of alternative remedies on the market that are meant to assist with erectile dysfunction but you need to take great care. Yohimbine, for example, seems to improve blood flow to the penis but controlled studies are inconclusive as to its effects. The American Urologic Association cautions against its use.
This link will take you to a good overview of natural remedies in relation to erectile dysfunction.
I have not tried many over the counter products but I have found Libimax to work well. It is a natural herbal supplement. The first time I used Libimax it seemed to work better the second day. But everytime after that it worked just as well the first day and for a few days after. I did not feel any side effects and it worked well so I would definitly recomment it. I found it to best priced on Ebay and www.bensbazaar.com. Amazon had it too but a tad more expensive. Good luck and I hope this helps.