Hello there - your account is missing because this is a completely different version of the site. The old FO3Underground is gone, more or less. It actually cost the old admins money out of pocket to maintain it - a problem this new version doesn't have.
The name change to GUN is a more complicated matter, but the short version is that there are people who have/had plans for the VGU 'brand'. When we were granted a chance to choose a new, free URL for the site, one of those people decided to insert himself into the conversation to remind us of those plans... in a less-than-friendly manner.
And so we decided to re-brand ourselves completely, freeing ourselves from any potential hassles and creating an identity which is 100% our own.