Hi and welcome to the Gigabyte Forum.
The first thing I would say is don't go messing with the BIOS settings or you could get in real trouble. Make sure that you understand what each option does before changing them.
I think the best thing for you to do would be to clear the CMOS first as we don't really know how the BIOS has been set up as it is a second hand machine. Follow these instructions please:
Remove the power cable from the mains supply and then press the power switch on the case for a few seconds just to drain any residual energy in the PSU capacitors.
Once done remove the motherboard battery for at least one hour before replacing it.
Next plug back into the mains supply and boot.
You will now need to enter the BIOS by pressing DEL and load Opimised BIOS Defaults.
Make any other changes to the BIOS settings to suit your self like disabling the floppy drive, disabling the full screen logo and making the HDD the primary boot device and then press F10 to save and exit.