Can I reuse my existing s-corp for a new business?

If I understand correctly, you started an S-Corp as the parent company of a retail business wholly owned by the S-Corp.  You then sold the corporate asset of the retail business, but maintained the parent S-Corp.  I’m assuming the retail business was a fictitious name/dba.  So, assuming that you have properly maintained the S-Corp with the state of Florida and it is Active, then, sure, on those facts, there shouldn’t be a problem using it for the tech start-up.  However, that is assuming there are no company documents that prevent it (and, if the s-corp was just you, I would doubt it).  That said, if your reason for using the S-Corp is just because it is there, I would caution you to at least consult with a business attorney (and perhaps a CPA) to discuss all of your entity options.  FL gives you several options and each has its own pros and cons – you could find a simple investment of time and money in the beginning may save you headaches, money, and time later.