Hello Adeodaantje, first of all I would like to apologize for so much trouble you are having with this product.
There are a few things that may have caused this behavior on your device.
Since the NUC came with BIOS version 0015, we always recommend customers to update the BIOS if they are experiencing an strange behavior on the product. But if the unit is working fine, no update would be needed.
If a BIOS update is necessary, the best thing would be to install the next BIOS version, in this case BIOS version 0021.
When there are a few BIOS versions between the original and the latest, it is better if we install each of them. Sometimes, the latest BIOS do not include the fixes of the previous ones.
Regarding the problem with your keyboard, that you cannot use it, we knew about this problem but we resolved it by a new USB 3.0 driver version. The new driver will be found on this link http://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=23734
Then, in regards to the operating system let me inform you that we this specific NUC support Windows 8 and Windows 8.1 64-bit only. There is partial support for Windows 7. We have received comments from customers reporting compatibility with Linux flavor OS, however Intel has not validated them.
At this point, what I would recommend you to do is to try to roll back to the original BIOS version 0015 using the BIOS recovery method.
Then, update the BIOS to version 0021, and after that please check the performance of the unit.
If you continue having issues you can always contact our technical support team for additional troubleshooting. http://www.intel.com/p/en_US/support/contactsupport