This scenario sounds so familiar. The short answer is--if you're not getting the results you're seeking after doing everything you mentioned, something's wrong. Perhaps the SEO is not on track, perhaps the forums you are blogging on are not the right fit.
Have you thought about what the interaction experience is like from your prospects' point of view? If all these are hitting a home run, then take a hard look at your website and shopping cart. If they don't look professional, if the website's hard to navigate, if it's a frustrating experience for a person to find what he or she is looking for--that could be what needs fixing.
Also, what other form of online advertising are you doing? A marketing professional can help you target the right audience, but here's how you get started. Decide on your geographic footprint, the age group(s) and the income level of your best customers. You can do your own due diligence on your target markets by conducting your own survey: where do they shop, what music do they listen to, what papers do they read, where do they surf the net?
When you have all this data, you can start to develop a sound plan to fix your site so that it resonates with those target markets, and you can blog, advertise, etc. in the right online venues. Once these are all in line, you might also want to consider a paid online marketing service, such as Hubspot.com, which regularly assesses the relevance of your website's keywords and content.
