was the floppy write protected maybe(move the little tab on the disk)
a floppy start up disk will not save you if a bios flash goes wrong.its dead motherboard time.
most bios updates are downloaded to a floppy disk and then you would have to set the floppy drive as the first boot device and boot from it to flash the bios.some new boards you can even flash the bios from within windows itself.
you will first need to know the EXACT make and model no.of your motherboard and download the EXACT bios update for it.the motherboard manufacturers website should have all the info you need to do this.
can i ask why you want to flash the bios?its usually only nesessary if installing very new hardware in an older system that otherwise would not work without updating the bios like a very large hard drive that isnt recognised properly for example.