Restart on plus sign

Hello!
i have installed macos catalina in my hp compaq pro 6300 sff.
i have updated the bios to version 2.99 and still the pc restarts after plus signs on boot.

the specs are:

i5 3470
8gb ddr3
gigabyte gt710
q75 chipset

plz help, it is very important to me

Author: ceshehan