I have done a fair bit of dating via okcupid, and I'm also a bit older now, so I have a pretty easy-going philosophy to it at this point. I can pretty quickly identify what I don't want, and if I see that in the guy I'm dating, that's it, there's not going to be a second try. I try not to dismiss people out of hand if there are no warning signs, but if I don't see it (or the other person doesn't), there's no need to prolong the affair.
I've done the no response thing, once. Perfectly nice guy, he didn't do anything wrong, I just didn't feel it and was in a mood to tell him. I felt very guilty about it, but it was definitely me, not him. People are capricious - it doesn't have to have been something about you specifically.
I've also been in the position of receiving a "so, did you like me?!" message from a guy after a really atrocious first date, full of stilted conversation, aggressive hugging, a split bill and a solo taxi ride home. I wrote him a very gentle email explaining that I just couldn't see myself dating someone who had a handgun (and I can't), but there were plenty of other warning signs there. He kept trying to contact me, and ended up reinforcing my first impressions. After the first response, I ignored him. I had already said my bit, and he wasn't listening.
You don't want to date someone who isn't in to you. It's a waste of your time and his/hers. You just need to understand that there's going to be a few meh dates for every awesome date, a few meh relationships before "the one" turns up.
I would say the odds of someone who has already ignored you once responding to a second message are slim to nil. Time to look elsewhere.
If you're using dating websites, I've had a friend suggest to me recently that using one that is on a pay basis (match.com) versus free (okcupid) might turn up more opportunities, because the people paying for the service are more invested in using it. If you've tried free and had no luck, and you have the cash to pay a little a month, you might try a six month membership with match.com and see if that gets you better results.
Above all, be patient with yourself and the process. It would be awesome if you could go on a couple dates a week and find someone right away, but what's the rush?