1. First off all you shall reinstall your Bios using recovery method, rather than Intel's tool. The easiest way to recover your Bios is to use the Power Button Menu method:
1.1 Prepare USB stick fully formatted (disable Quick format option during formatting) to FAT32 with Bios file RY0367.bio Download BIOS Update [RYBDWi35.86A]
1.2 While NUC is OFF insert this USB into USB slot.
1.3 Press and hold the Power Button (for about 3 sec). You should release the Power Button soon as the power led changes color from blue to amber. NUC will reboot into Power Button Menu. With the USB containing the latest bios file, press F4 and the recovery shall start.
1.4 After recovery is competed, pull out the power cord from the NUC, remove the USB and after replacing the power cord, power ON your NUC.
2. If your computer is still slow, you shall look for problem in your Windows installation:
2.1 Check all your startup items and disable all unnecessary items.
2.1 If still your computer run slowly, my suggestion to you is to repair (replace) your Windows. It can be done very easy with an in place Windows upgrade. Please follow this tutorial and your Windows will be replaced without loosing anything (all your personal data and your application will be not touched): Windows 10 Help Forums .
Hope this will help