Hello and welcome.
Ahhh I see what they did.
The BIOS has been set to boot from your network adaptor.
Are you able to restart the machine and enter BIOS/Setup?
That is restart and press F1 key.
Locate Boot tab and set your boot order as follows:
Hard drive.
CD/DVD rom.
Make your network adaptor Realtek the last one or turn it off so your machine will not boot from it,disable boot from LAN.
Save and exit.