I have had my Inspiron 15 3000 series since the end of August and was liking it until is started beeping a few weeks ago - sounds like a truck backing up. It does it 5 times and repeats 3 times when starting up. I tried online support but you cannot get anywhere until you enter your service tag number or express service code neither are recognized. I tried calling support but they could not identify my computer with the numbers either (I took pictures of them on my tablet and made them larger so I know they are right). I purchased my laptop on line. Initially there was a message about the power source, but I have popped my battery out and back in and the error message no longer pops up but is still beeps. I am at a complete loss as to what to do at this point and am incredibly frustrated.
Ran into the same brick wall you did on the codes issue. Sorry you are experiencing that, but glas I am not alone in frustration.
BradyMommy wrote; "It does it 5 times and repeats 3 times when starting up."
Five beeps usually mean Real Time Clock (RTC) power fail. I'd suggest you replace the CMOS battery in the system. You can purchase a brand new battery at your local Walmart for about $3.00 -$5.00.
To get a better understanding of Dell beep codes, please click on link below. The Dell article also apply the same as to most Dell laptops.