This is going to be a long ass post, so you can try to chew through it, or just take it to somebody who has dealt with this kinda of shit in the past.
So first off, you need a way into the router, using one of the following:
Added a few different ways this can be done.
First off, get a software called Putty or Tera term, both are easy to use, i prefer tera term because you don't need to set baud every single time in configuration, keep in mind default baud for cisco routers is 9600.
http://en.sourceforge.jp/projects/ttssh2/releases/
Next up, we need to get access to the router, this can be done multiple ways,
Easiest is using TCP IP, using SSH (if this does not work, meaning SSH is closed off, scroll to the end...)
Hit in the Host (router IP) and connect, or if you are using Serial *COM port, choose the correct one, you can check witch one you are using in device manager)
Hopefully you got in, now enter the username and password (should be cisco / cisco)
Type in command "show flash"
There should be atleast 2 files by default, one should be
bigassstrangefilenamewithnumbers.M5.bin
and startup-config
Since this damn thing does not have a USB slot, it makes things hard, meaning you have to use TFTP to transter the files from your computer to the router. For that you need tftpd32
!NOTE all firewalls must be turned off!
Now you are sharing a folder through the TFTP, put your .bin and configuration files into it that you want to use.
type in copy tftp://yourcomputerip/filename.bin flash://filename.bin
(example copy tftp://192.168.1.10/CiscoStartUp.cfg flash://CiscoStartup.cfg)
next up, show flash,
see that your file is now in there and do command
copy flash://CiscoStartup.config nvram://startup-config
after that command "reload" now router will ask you, that if you would like to save the changed configuration, DEFINETLY NO, because it will overwrite your changes because it saves running configuration with start-up configuration and the one running right now is broken!
now that was for the configuration update, if you needed it. i placed this here first, because it gives you all the neccesary tools to do the IOS image stuff that comes
How to copy a CIsco IOS image from tftp server to router step by step is shown here:
http://www.cisco.com/c/en/us/support/docs/ip/simple-network-management-protocol-snmp/7910-11-7910.html
COM port to Ethernet (plug the ethernet one into the Console plug located on the back) and the COM port into your laptop, now since most systems don't have that, you need a USB to COM Port cable.
!you will also need the drivers for usb to com port adapter, i had to use Vista drivers for the thing to work, and install them using compatibility mode.