CISCO 2921 router

[G3261]

I need help re-Cisco 2921 router...which I believe I messed up....initially, I couldn't login to the router after changing the initial password but I managed to get that working. I can go to # mode now.

some how, I copied startup-config to running-config and  saved it. Obviously, that has been creating some problems for me. My question is-if I erase my statup-config and RELOAD the router, am I going to lose anything critical? Specifically, any licencing info etc.? My Team Leads always told me NOT TO reload the routers because it has some critical info in running-config!!! I would really appreciate your help in this matter (I am a newbie in this field). 

I would like to start again from scratch...is there anyways I can have this router back to where it was when I opened the box?

[Leo Laohoo]

My question is-if I erase my statup-config and RELOAD the router, am I going to lose anything critical? 

You lose EVERYTHING.  "startup-config" is the configuration file.  So if you erase that, it's gooooone.

[Paul Bundschuh]

You would lose your config, but not your licensing info, since this data in in flash memory. According to

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3750-e-series-switches/QandA_Software_Activation.html

Q. Where is the software license stored on the switch?

A. The license file is stored on a special area of the flash memory in the switch. The license file is not directly viewable within the switch's file system, but the CLI exists to view and manage the license file.