I had to reinstall my system on my laptop Lenovo G510.
I can understand you re an inexperienced user. So, let s start with the simple things first because it could be a number of reasons.
If it was working before it should also work now. So, did it work before? If YES, did you follow EXACTLY THE SAME STEPS to reinstall it?
You mention Windows 8.1. Was your previous system dual booting? Could you boot in either OSs (Antergos/Windows)?
after the reboot and removed pendrive shows up “No bootable device - insert boot disk and press any key”
You mean you booted with the pendrive on and THEN you removed it? Maybe it booted from the pendrive and when you removed it it could not find it?
Also, are you sure you did not install the GRUB in the pendrive? Did you check where the GRUB was installed?
Take a look at all the above possibilities for now and let s hope for the best.