You've said you purchased it a month ago, and in the same post, mention a week.  If the system is less than 30 days from shipment, return it for a refund.  Otherwise, warranty repair parts are considered refurbished (and by every system manufacturer, not just Dell).  Have the fan replaced and the system should function just fine.  
I just bought a brand new m15 R5 a month ago. I started using it a week ago. It was a gift and came early. I've used it only on a cleared desk because I've been nervous, as I never owned a computer this expensive before.   This morning, I was getting some work done and it shut off. I turned it back on and it came up with a fan error 2000-0511. I went in and ran the online system check and came up CPU fan and GPU fan not responding.  The fans don't appear to be running at all because it's completely silent. I don't hear any and gets hot with use. I updated all drivers etc listed in support assist and reset. The 2000-0511 error remained.I opened a case with support. They instructed me to use compressed air to clean debris. I did that. Well, best I could. I couldn't get all the screws loosened to take the back off to do it. All but 3 came off but the last 3 just wouldn't. He said just to do it through the vents so I followed his instructions.They told me to go into BIOS and choose optimal defaults. I did and still got an error, this time 2000-0712.  Still not working.I'm frustrated because despite always having bought cheaper computers, they've always lasted for several years at least, and then I have a problem with this one that still isn't rectified after hours with support a week into using it.  Why would a new computer fan to just stop with nothing having happened and is there anything else I can try?
m15 R5, CPU/GPU fan not running?