After you answer islander's question, it would help if you knew what software your menu was. This is called a dashboard. Likely dashes are EvolutionX (many call this "slayers" as it was used in a popular auto-installer but as far as I am aware it is really just EvoX underneath), Avalaunch, UnleashX or even XBMC.
You will probably need to download the desired dash from xbins. Link on how to use xbins is in my sig.
To get back into your box you will need to have a CD/DVD you've burned with software on it to allow FTP access to your box. Tutorials on this at Xbox-Scene. (x-s)
So long as your BIOS is still OK and allowing you to run unsigned code there shouldn't be much difficulty in recovering. Just going to be a few steps, and depending on what has happened to your box the menu may not look the same when you're done. Hopefully it will be better.
-Whoopin'