First, clear the CMOS and see if your system completes POSTing. Look for a jumper on the motherboard for this function. You must unplug the computer first.
By the way, which motherboard do you have?
If it doesn't complete POST do you at least see an option to flash the BIOS (on some motherboards you press ALT + F2)? If this option is available then all you need is the BIOS file on a floppy disk to re-flash.
If neither of the above works then you need to replace the BIOS somehow. Usually you can just contact the motherboard manufacturer and get a BIOS replacement chip. (Abit charges $12-$14 here in the USA. Don't know about other manufacturers).
There are services that will replace or reflash the chip for you. Sometimes less than the manufacturer charges. I'll update with links later if desired.
You can take your motherboard or BIOS chip to some computer stores and they will reflash for you. I think they charge similarly to the manufacturer.
If you have another motherboard with a similar type and size (size is important) BIOS ROM you can attempt a "hot swap". Basically you just loosen the BIOS chip on the other motherboard and boot to DOS. Next, you remove the BIOS chip with the system still powered and swap in your BIOS chip that had the failed flash. You can use a program called Uniflash which can force flash the BIOS even if the donor motherboard is a different brand/type. Return the chip to the original motherboard and hopefully it will POST.
<b>I have so many cookies I now have a FAT problem!</b>