Co-founders can't be convinced that we need investment

Our start-up has changed direction three times, but after more than 24 months we still do not have a saleable product or even a working prototype. Despite this situation, I can't convince my co-founders that we need external investment to shorten the time to market. Instead, they are only interested in government programs with lengthy application procedures or simply in making do with subpar equipment and tools, which also means that we constantly fail to meet deadlines. Besides, we are working without a salary, which I do not think is acceptable anymore, how should I proceed?