Your entire load is broken. That's what's going on.
Do this... disable every addon except nUI... this includes disabling *ALL* nUI plugins. Log in to WoW. Does nUI load correctly (unit frames, chat frame, etc.)?
If it does, then we know it's an addon.
Look at the version that's being printed in the chat frame... if it does not say "nUI 5.06.25 has been loaded" then you have the wrong version installed... go get the latest version.
If nUI does not load, go to the [ World of Warcraft ] folder and rename [ Interface ] to [ Interface.saved ] and renamed [ WTF ] to [ WTF.saved ] -- log into WoW and at the character selection screen, go to the "AddOns" button. Are there *any* addons listed in the screen? If there are, then you are working in the wrong WoW directory.
If there are no addons listed, close the addons window and enter the world on any character then immediately exit WoW. Install the latest released of nUI in the [ World of Warcraft > Interface > AddOns ] folder then log back into WoW... does nUI load now? (It better!)
Once you know nUI is loading, you can start reinstalling your other addons one at a time... try installing the addon, then logging in to make sure nUI didn't get borked. If it did, then we know which addon is causing it.
----------------------------------------------------------------------------
Simple outline...
- Make sure you have nUI 5.06.25 or newer installed.
- Log in or out to your character selection screen in WoW
- Click the "AddOns" button
- Click the "Disable All" button
- Scroll down until you see "nUI" and enable it
- Close the window
- Enter the world on any toon
nUI should load correctly now. If not, let me know.
If it does, start enabling mods one at a time until it breaks, then we know which mod the conflict is with.