The first thing I would focus on is:
My web site received about 2000 people in 3 weeks and only 1 purchased
a copy of my software.
and ask the question why only one?
Two possibilities come to mind, the first is that the ads are bringing people who want something other than your product and second the ads are bringing people who do want something like your product but when they get to your website they don't think your product meets their needs.
Let me give an example, suppose I am looking for a bookcase to store my movie DVDs and I Google "video storage" and your ad pops up with something like "Worlds greatest video storage solution" so I click on the ad expecting to see a storage cabinet but when I get to your site I see it is software. This was a wasted ad and you will never sell this person.
Now for a second example, suppose I am looking for software to help me catalog my videos and I get to your website via an ad and when I start checking out your product I find it only runs on a Mac but I have a Windows computer. Once again no sale. This time it is not that I don't want a product like yours, it is just that your product does not meet my needs (a program that runs on a PC).
The way to determine which category a visitor falls into is via Analytics (Google Analytics is free and widely used). The former class of visitor will immediately leave your site as soon as they see that your product (software) is nothing like what they are looking for (furniture). The other type of user who is looking for software will generally spend more time on the site, at least long enough to see if the software meets his needs.
Probably the best you could hope for with an optimized website and optimized ads is a 1% success rate (that is 20 purchases out of 2000 visitors). Some people do better, but most people would be extremely happy with a 1% rate. You are getting 5% of that (1 purchase instead of 20), so you definitely have room for improvement.
So you are left with the question Is it the ads, is it the website or possibly is it the product? If you think your product is good enough, then my advise is to keep at it at least long enough to get some meaningful analytic data and understand what is going on.
Even if you decide to give up on this product in a couple of months you will have learned a lot about internet marketing, response rates, analytics etc. which will be invaluable in launching your next product.
Finally one question: Do you have a free trial download so that people can try before they buy? If not, consider adding such a trial to the website and see how many people download the trial.