how to revert running config saved on PC

Changes applied to the running config are edits that modify its current state. It is therefore /not/ in the general case possible to go back by applying the config file to the running config. You probably tried this :-)

There are two stratigies:-

1. Modify the running config so that it ends up as you like it. This will require creating a set ot edits and applying them.

conf t int a no shut int b ip address x.x.x.x w.w.w.w

Creating these edits is a manual process.

1. Replace the startup config with one you like and reload the router.

a) copy tftp start

The file can either either be one copied off with tftp or can be the text file displayed with "sh start-up".

In general the file seems to be pretty robust. Bad things are ignored and DOS and /Unix text files are accepted.

b) write erase ! blow away startup-config reload ! Get factory default running-config.

Apply edits to running config. i.e. conf t !! paste in config file

In ALL cases "copy run start" afterwards (or wr) for those that have an aversion to typing.

tkdiff is your friend for comparing configs. You need say "Active TCL".

I have almost no experience of method a).