Couple points:
You need to determine if the product/idea is actually viable and the problem is in fact that the other founders are failing to execute, or
the is is something inherently flawed with the business model. Have some entrepreneurs or VCs you trust and respect review the business and give you their opinion.
If the problem is the other founders, you could start talking with them about bringing on someone to turn the company around or about selling the company to someone else.
If the problem is the idea/product/business model, you should move on ASAP.
In either case, if there is some useful technology that can be repurposed for another idea/business, make sure you get a unlimited license or if the company folds, take ownership the IP assets as back unpaid salary.
Make sure you get the transfer of IP in writing, ideally reviewed by a lawyer. If you do build something successful with the IP, you don't want "the idiots" coming around and claiming they own part of it.