Usually there is 3 pins next to the battery on the motherboard and one jumper on it. This jumper has two settings. Normal and Clear. Moving the jumper to the Clear setting will erase the settings stored in CMOS. It does not remove the BIOS itself.
At the min the jumper should be on Normal. (pin 1+2).
Change it too Clear (pin 2+3).
Then boot up. When you clear the CMOS you will most likely see the error message "CMOS Checksum Error" on the next reboot.
Thats Normal. Just Hold the Power button and turn the PC off.
Put the Jumper back to Normal (pin 1+2) and reboot again.
Enter the BIOS and you should be able to reconfigure everything from there.