Hussein, where are you from?

Can you plz mention what is hardware version of your router?

Morry wrote

@Deniss:)
It sounds unreasonable that router's LAN ports don't like PC's ethernet port.
Did you try all the four LAN ports with your PC?
I think it could be a problem of the cable you use, or the LAN port on the router, also the ethernet port on your PC. I do suggest you test with another laptop. If you have the same problem with the laptop when it is connected to router's LAN interface, it probably is a hardware problem on router's LAN interface.

As I already said, I tried everything.
When I turn on or restart pc, lan led on router is off. Then, I must unplug cable from router or netwotk card and plug again, and it works.
After all, I think that problem is RTL8111B PCI-E Gb LAN controller on ASUS P5LD2 SE, but it works fine without router.

Hussein, from your post, i am a bit confused..
1. " Authentication error occurred". This authentication error occurs when you remove the network from the list, search the network, when it appears, connect it and enter the WPA key...I am wondering have you entered the correct password? such a stupid question..But you'd better make sure the case-sensitive wifi key has been entered correctly.
2. "The only way to connect wireless was to either Reboot or power off and then Power on the router" It seems you can successfully connect to the wireless network. But the connection drops out? How many wireless client do you use to connect wifi at the same time?