When the Bluetooth icon disappears, that indicates a problem with the Bluetooth drivers.
When that happens again:
1
Open Device Manager (accessible by right clicking your Start Button)
At the top of Device Manager, choose View - Show Hidden Devices
Does that show hidden Bluetooth device(s)
if so, right click and uninstall that
Restart your PC
Check if Bluetooth is then working
2
If Bluetooth is still not working, go to the support page for your PC on the manufacturers website, then from there, download and install (not update) the Bluetooth device drivers they recommend.
If you have any difficulty locating that support page, click your Start Button, then just type msinfo and press Enter, please provide a screenshot of the resulting System Information window.