Thanks for making this post. We've not had an email from you, or its been spammed. We dont offer a phone service - you'll see details of why not here: https://secure.ups-trader.co.uk/contact-us
I'll respond here and then try to find your email and forward it that way too.
OK the UPS is SMC1500i tower UPS you say you have tried two power leads and you have plugged in the battery isolator.
This covers the basics. Noting you are hearing a hum so its not stone cold dead.
If you are happy to do so can you take the front of and check 1/ The ribbon cable to the LCD panel is attached OK. 2/ Inside the battery flap, are the battery leads all securely attached.
You can also share a video of whats going on. I'll show it to the warehouse and we might might spot something that you have not seen.
If nothing comes from that we'll be moving to swap this out for you so we can investigate further our side.
Last thought, take the battery isolator out again, and look into the reciever. Check the pins are still there. They can be pushed backwards and not be mating with the male connector when its plugged in.
At first I thought it was the front mounted LCD panel that you had found a loose cable on, but now think its the daughter board that sits inside the UPS, under the main board and near where the LCD ribbon goes. I'll open one and take photos and add below.
I think it was just vibration in transit that worked it loose, and that will be it. I note APC only use two retainer posts rather than 4x, but they do have separating pins to supposedly lock in place. Were these still holding?
There is the 12 month warranty to fall back on.
We will also get these small boards in stock when we scrap units. I can ship one out to you free of charge if you'd like one on the shelf,but I think you're in the clear now.
I'm going to refund you £20 to say thank you for taking the time it took to investigate your side.
My pleasure. My best guess is that the left side split riser (white thing) was never fully pushed through and locked. Let me know if it gives you any more trouble Seasons greetings -NB