StoutFiles - 5:47 pm on Feb 28, 2011 (gmt 0)
One sale a day isn't a big enough number to accurately suggest that something's going on if there's a lull in sales. Three weeks is a large time frame, but it happens.
Have you used a proxy server to see what the search results look like from another area? Google changes ranking based on area.
Have you bought something yourself? If you think the purchasing system is "hacked", buy your own product on your website to confirm.
If you're worried your server is still messed up, ask the host to clean it off and re upload your files/databases.