There are two BIOS sizes, if you unsuccessfully flash the wrong size the card will no longer POST but it will work as a second card as it stupidly zeroes out the BIOS before checking if it's the right one. The only way to fix the card (without directly programming the chip) is to put a PCI or ISA video card alongside the Voodoo3 so the computer will POST, then run the BIOS update again with the correct size BIOS file.
I accidentally did a bad flash myself but was able to flash it again by burning the correct file to a CD and performing the update before restarting the computer. I also have a PCI S3 Virge card that I could have used as a backup.
98/DOS Rig: BabyAT AladdinV, K6-2+/550, V3 2000, 128MB PC100, 20GB HDD, 128GB SD2IDE, SB Live!, SB16-SCSI, PicoGUS, WP32 McCake, iNFRA CD, ZIP100
XP Rig: Lian Li PC-10 ATX, Gigabyte X38-DQ6, Core2Duo E6850, ATi HD5870, 2GB DDR2, 2TB HDD, X-Fi XtremeGamer