First look at the pens, there is a light in the center of the pen. This will tell you what state the pen is in.
If the pens are showing a red blinking light or solid red light.
Turn off the pens and charge them. They have run low on battery.
If the pens have a blinking green light.
The pen is in discovery mode and need to be paired with the system. Open the Bluetooth menu and select "Add Device". This will put the system into discovery mode. The pens will show up as an input device. The Bluetooth password is 0000.
If the pens are showing a green light and are still not working.
Next make sure that the pens are connected to the correct device. Open Hoylu Central and see if the pens are being shown as connected. If the pen does not appear in this menu, check the Bluetooth for the system. Go to the system trey and open the Bluetooth menu. This will show you the current active Bluetooth device connected to the system. If the pens do not appear you will need to reconnect them.
If the pens are there then you may have competing Bluetooth receivers on the PC. To check for this open search (Cortana) and search for "Device Manager". Once the Device Manager open navigate to the section labeled "Bluetooth". Open this section. There should be a single "Generic Bluetooth Receiver" in this area. If there is an additional one labeled "On-board" or "Integrated" then you need to disable that one. Right click on the device and click 'Disable'.