The question is whether the person in charge of the company really wants you to find out and come up with a clear picture. If the owner of the business is not giving you full support, you are fighting a battle already lost. Been there, done that.
Your initial focus is on "stop the bleeding". Take over the control over "cash". Implement procedures that regulate/limit signatory powers and restrict the use of Credit Cards to certain sectors (gasoline only etc.) Take over control of the incoming mail to avoid that vendor/customer reminders and claims "get lost" in the process. Nobody can purchase without an approved purchase order. In a company, cash/bank signatures/credit cards/ and purchase orders are like the "watering hole" in the jungle. Sooner or later, everybody will show up. Equally important is the billing/receivable department. Have all sales/services been billed. Is somebody lagging in working out the input needed for the billing? Look for company registration documents, tax filings, bank and credit card statements and obtain a credit report You might find existing liens and collection issues
It will take you less time than you think to get a good idea of what is going on. But once again, it only works if the person who has the ultimate decision power of the company is expecting and supporting you to clean up. Otherwise, it will be you who becomes "the problem".