Locked FSB speed

Hi, I have an old Compaq Deskpro EN 6350 computer, with a PII (Deschutes) 350 MHz processor, chipset Intel 82440BX/ZX, FSB 100 MHz, 192 MB SDRAM and I would like to overclock to work at 500 MHz. BIOS is updated to the last revision 08/22/99. On my motherboard there are 6 switches for setting the FSB at higher speeds, and I have turn them on to run at 500 MHz, but nothing happened. It’s seems that my motherboard has the FSB locked. Any ideas how to unlock the FSB setting?