You bought your PC with a 500gb HDD with the intention of installing your own SSDs, if I recall correctly?
What's Windows currently installed on?
The PCS logo and the spinning wheel is Windows loading. Unlike Windows 7 where you had the MS logo, in Win 10 it shows the OEM's logo. I'm not sure why this kind of change was made but if I had to don my tin foil hat and guess I'd say it's because Microsoft didn't want people to blame Windows for slow PC startups but rather the PC manufacturer. Or maybe PC manufacturers badgered MS to let them show their logo for longer than just the POST screen.
So if your Windows is still installed on the HDD, I'd put it on an SSD instead and see what difference that made.
PCS will generally provide you with the spare accessories from the motherboard's box. The Z270E ships with 4 sata cables. With your spec here (https://www.pcspecialist.co.uk/foru...stomer-service&p=389299&viewfull=1#post389299) you use 1 for your HDD, 1 for a DVD drive. So I'd have expected 2 spare black sata cables to be in the welcome pack box that shipped with the PC.
the only spare cable in the box looks like a GPU power cable .there are some cables in the case the wider plugs but cant see any power ones .wider ones are on the same cable that powers the HDD and DVD drive
The PCS logo is part of the BIOS (it's the splash screen) and it stays on during the POST (power on self test) and until the OS is started. You could go into the BIOS and set the POST to run the minimal tests, that will reduce the time the PCS splash screen is displayed, but I prefer to have all the POST tests I can get!
The Windows 10 rotating circle is Windows way of letting you know that it's booting. Most of this is program loading and the speed of your hard disk has the biggest impact here. A slow disk will result in a slow boot. An SSD as your system drive will make a big difference here.