I noticed that you first talk about your professional experience as a "sales engineer and industrial electrician", but then you refer to it as "technical and project management experience". Those are all different fields, and I'm not sure how Project Management fits into this. This gives the impression that you are all over the place, and I think some clarification here would be helpful.
My Advice
1) Tie everything back to project management: As I said, it's unclear to me how project management fits into your work history, or your future goals. But if you did work as a PM, and you are interested in pursuing that again, I think it should be fairly easy to tie your startup experience to project management.
Project management is a big field that covers many aspects, and I think running a startup requires a lot of the same skills that a PM needs - managing resources, scheduling, budgeting, customer support, documentation, etc. Explain how running your startup helped you improve these skills.
2) Create multiple versions of your resume: I think it's good that you have experience in various fields, as you can leverage what you've learned in one area and apply to another. You can bring a different perspective to things because of your insight into other fields. That said, when you apply for a job I don't think you want to appear as a "jack of all trades". You want to show and prove that you are a master at whatever job it is that you are applying for. If you are applying for a sales position, you want to highlight your expertise in sales. If you are applying for an engineering position you want to highlight your experience in engineering.
Taking that into account, my suggestion would be to create multiple versions of your resume. You want to include all of your experience on each version, but you want to modify each one to focus on the area that the job you are applying for requires. The reason you want to include everything is because a gap in work history looks terrible on a resume.
As an example, let's say you are applying for a sales position. Include both your corporate experience as well as your startup experience. The work you did in your corporate sales position will be easy - include all of that. Now for your startup, you probably didn't have the official title of "sales" - you probably used something like CEO or founder. But that doesn't mean you didn't do any sales work. I'm sure that like most startup founders, you did it all. So under your startup work history make sure to highlight what you did in relation to the sales part of your startup.
3) Demonstrate lessons learned from your failures: Your startup failed, so what? We all have many failures under our belt. The important thing is to learn from your mistakes. The worst thing you can do is blame something else for your failures. Take ownership of them - ultimately they were your decisions, so you are at least partly to blame. Explain what you have learned from your mistakes, what you would do differently, and how those mistakes influence the decisions you make from now on.
4) Have your resume reviewed by others: Ask friends and family to review your resume. A lot of times when we are so close to something we tend to overlook the obvious. Also look for local organizations that do resume reviews. Possibly a local university, or even your local SCORE chapter.
