CTO vs. VP of Engineering
cpierret: New CEO probably thinks that the engineering team is a mess and someone has to fix it. 
Stop implementing Nagios yourself (and any non business critical issues), and ask the CEO for some freelance to do the job instead.  If he argues that he has no money for that, run away fast (he has money to hire a VP Eng...). If he agrees, then start building a trust relationship with him quickly.  Tech tasks usually can wait, where your CEO cannot (yes computers are nicer than CEO, but CEO signs your paycheck)
Focus on customer needs and your colleagues' need: how can you help sales/presales and marketing do their job ? Ask them what they need to succeed and give them the product they need. If you cannot because you don't have the resources, be clear about it and have them decide which tradeoff with you (or have the CEO allocate more resources).  Become accountable: Learn to say "No" to mission impossible and avoid saying "No" when you could if you had more resources, just say "I could if ..." and have them participate in the tradeoff decisions.  Write things down once the decision is made and email it after the meetings.  If you think that this is too late for that, or that the sales/marketing guys have no clue (or are trying to cover), quit... and start again elsewhere.