I have a GFCI outlet in the kitchen that shows no LED color status, cannot reset but still has power, but no power downstream. Does it mean I have a bad GFCI outlet and need to replace it? or I need replace GFCI and downstream outlets?
An aside first: if it's not your plan to protect the downstream outlets, don't use the Load terminals at all. The instructions also state how to put 2 wires on "Line". If you do wish to protect downstream outlets, identify them per instruction 8(C). You don't need to use the provided blue stickers; any marking will do as long as it's not hand written. I use a label maker myself, and state where the GFCI reset is to be found.
Even though it's AC, the GFCI mechanism is directional.
I assume "has power" means "appliances work". A normal GFCI that is tripped will knock out both the GFCI's own sockets and the downstream loads and receptacles.
The #1 installation mistake with GFCI receptacles is reversing the "Line" and "Load" terminals.
On older GFCIs, the sockets will work but the downstream outlets won't, because the Load terminals are hardwired to the sockets proper. They are totally unprotected. The symptom is "Sockets work, won't reset (and won't trip with a GFCI tester)".
On newer GFCIs, they have a feature specifically to detect Line/Load reverse. The unit will not work at all.
My advice when installing or troubleshooting a GFCI device: connect the "Line" terminals only. Make a testing checkpoint there. Power the circuit back up and run the GFCI through its paces. It should power up, reset and test, and if it has sockets they should work. After that, power back down and attach things to "Load" terminals. Now you know if the GFCI fails it can only be the stuff you added.