The exact same thing happened to me today. Someone online suggested that my computer might be hung up on system resume. For some reason the system resume wasn't waking up the monitor (no hdmi signal), and the keyboard appeared to have no power. My mouse was only momentarily powered when i turned the computer on, then the mouse light went off.
The trick for me was to clear out the system resume. Apparently the system resume is stored in the computers RAM/capacitors, so it says with the computer even if you turn off the computer and unplug it.
To solve this:
1) Turn off computer and unplug
2) While the computer is unplugged, hold the Power button for like 20 seconds. This will clear out the RAM.
3) Plug in computer and it should work.
Hold the F8 key for safe mode. I didn't try this myself, but I heard this worked for other people even when their keyboard seemed like it didn't have any power.