Thanks your answer!
We use 3400 and 3750 switches in our network.
And I would to know: what does mean if the port status LED is green or amber, maybe it doesn't light?
Find information on the 3750 here
For ports, in the default (port status) mode, the LED colours mean as follows
LED Off : Port disconnected or administratively shut down
LED Green : Port link active
LED Green flashing : Port active (data flowing)
LED flashing green/amber : Link faulty. Port receiving errors - CRC, excessive jabber, alignment errors etc
LED Solid Amber : Port blocked by STP (either in learning mode or blocked owing to dual path), and not forwarding traffic
LED Blinking Amber : Port blocked by STP and sending/receiving packets
The information for the 3400 switch is here
But the meanings are pretty much the same as the 3750.
(Please mark question answered if it is to your satisifaction)