will the same ISO for a cisco 802 work for a 831?

okay this is my problem... i've got a cisco 831 router that will not boot from falsh the nessage i get is

boot: cannot determine first file name on device "flash:"

or

boot: cannot load "flash"

okay when i try to view the flash contents i get a message that is like this

rommon 5 > dir
usage: dir <device>
rommon 6 > dir flash
bad device name
usage: dir <device>
rommon 7 > dir "flash"
bad device name
usage: dir <device>
rommon 8 > dev
Devices in device table:
id name
flash: flash


it will only load in rom monitor and i cant seem to get out of it no matter what i try... any suggestions or maybe even any copies of an new ISO would be appresicated...