First be sure you have your SHSH blobs backed up.
If you have your blobs backed up you can restore to any version of the factory firmware for which you backed up the blobs.
Blobs are personal and specific to each persons AppleTV2 you can't use anyone elses.
If you forget or don't backup the blobs before Apple releases a new version of firmware, the blobs can never again be backed up, the opportunity is missed.
Sounds like the greenpois0n jailbreak wasn't finished.
Suggest restoring to factory fresh firmware version 4.1.1 and jailbreaking again.
1. be sure after greenpois0n says "Completed" do not touch anything for 1 minute
2. for extra measure after clicking to close greenpois0n do no not touch anything for 1 minute
don't trust your intuition, watch a clock, the jailbreak is known to take up to 40 seconds after completion to finish writing stuff to the AppleTV2 nram
if the jailbreak is broken, it can "appear" to function to a degree, which can be misleading