GA-EP45-DS4P @ Lan Port 1 NOT Working

I have problem with GA-EP45-DS4P Lan 1 port not working; when I connect to internet ( the network cable CAT 6 connect directly from cable modem to LAN port 1 on my GA-EP45-DS4P ) the error popup with yellow exclaimation mark in task bar, clickeds on it and error said:
" your Internet connection is very limited or no connection at all ".
Here is another weird thing :
If I take the same Network cable plug into GA-EP45-DS4P Lan port 2 then it is working fine !!!
Also notes here: I have 3 computers in my house with the same problem:

1) First computer using ASUS P5WDH DELUXE mainboard
connect directly to Motorola SB5101 Cable modem
Also had the same problem on Lan 1 Port ????

2) Second computer using ASUS P5Q DELUXE mainboard
connect directly to Motorola SB5120 Cable modem
Also had the same problem on Lan 1 Port ????

3) Third computer using GA-EP45-DS4P mainboard
connect directly to Motorola SB5101 Cable modem
Also had the same problem on Lan 1 Port ????

I read the reviewed on the net somewhere ( I could not recall where) :
The two Gigabit lan ports on motherboard they used two chipsets:
One link to PCI Bus
One link to PCI Express Bus
One is higher bandwidth transfer than the other

I don't know why all my 3 computers can NOT using Lan Port 1 ? If I switched to Lan port 2 then they all are OK ?!
I am pulling my hairs out try to figure out why is it, and I am very frustrated !
I would appreciated very much any helps / solutions or suggestions to solve this problem !

here are the specs of my GA-EP45-DS4P computer:
no overclocking, all run at optimized default !
BIOS version: F6B
Power supplied: PC cooling 1200 Watt
Video Card: ATI 3870 x 2 PCI Express Graphic card
Processor: Intel Q9450 Quadcore
Memory: 4 x 2GB=b Corsair Dominator
5-5-5-15 2T Timing
Controller: 3Ware 9650SE-8LPML 8-Port Serial ATA
Master: Seagate 1 Tb using WinXP Pro 64
on SATA controller 1
4 x 500 GB Seagate Raid 5 on Raid controller
LG DVD Burner on SATA controller 3
Pioneer Burner on SATA controller 4

Thanks in advance for any inputs !

After Numbers of tried, I found the cured for all of three computers just a simple solution:
* for the low bandwidth tranfers port I use short network cable CAT 6 like 1.5 m or 3 m
* for the higher bandwidth transfer port , I use the longer cable CAT 6 like 25 m .
Or vice versa !
And then BINGO ! No more problem for me !
I don't know why but it worked ! Whew.....