Leon, I've done several re-installs over the last few days on some used laptops I got - I bought two and was given two. As Mark said, download the Media Creation Tool and make a bootable Win 10 install on the USB. You can make it as a 64 bit only or 32 and 64, in which case it will give you a choice when you boot it. If you're doing a new install you'll need the alpha/numeric key that came with the PC. If you can't find it this programme will -
https://www.magicaljellybean.com/keyfinder/
To use the boot drive you need to go into the bios to set the USB as the boot drive, restart and it should boot from the USB, then just answer the prompts and away you go, it will wipe everything and do a clean install. When it's finished it may restart again at the initial prompt from the USB, if so just go into the bios and change the boot to the hard drive.
Edit:if you've got more than one partition it will show this and you'll have to select which one you want to install it on, in my case(s) I had multiple partitions and I just used the "remove" option to just leave one.
When it boots from the hard drive you will then have to go through the setup procedure and it will give you options for installing all sorts of things!! Just read them carefully and don't tick any of them, it's all rubbish!
There are also videos on youtube that explain how to navigate through the multitude of settings and turn off a lot of things that Microsoft kindly install and aren't necessary. The first thing I do is go through all the apps that appear on the start menu and uninstall the obvious ones that simply clog things up (like the solitaire/games crap) - right click on them and you should see "uninstall". It's time consuming but rather satisfying, removing the bloatware that Microsoft installs.
