Why my Y-wire undetected?

[Su]

With nest expert, i installed my nest thermostat without problem by my own.  But then, my nest thermostat says my Y-wire is undetected and not enough power from c-wire.

please help me figure/fix this problem ASAP

[Jeff]

Hi, everyone. 
In an effort to keep content fresh on the forums here and prioritize current issues, I'm going to go ahead and close up this thread. If you have any outstanding issues from this post or any other problems, please feel free to open up a new discussion.
Thanks,
- Jeff