hi,
bad news, but don't despair.
do not power down the router
do not reboot it
copy the running config to a pc
(run a ftp server on your pc)
(copy run ftp)
(give the ip address of your pc for the ftp)
(accept the default destination name)
(transfer, open file with a text editor for control)
(SAVE THAT !)
if you have an active smartnet contract on the software, you can have a CCO (access to cisco web site) that would allow you to download the IOS.
if you have not, try to contact the company that sold you the 2621.
or buy from cisco the needed IOS (basic, vpn, voice, ... there are many variation, so better ask an integrator to help you here)
or copy (ftp) the flash content of another 2621 (if you have)
other means might not be legal
if you did reboot or power down, there should be an (old) minimum iOS on eprom. use it to access the router and to use BASIC IP routing (best that than nothing) and FTP all files to the flash. FTP also the saved config file
when all done, do a "copy run start"
(older ios its write mem i think)
good luck
jacobson