Weird modem issue

[Phobophile]

Hi,
i recently did a fresh Windows 7 HomePremium x86 install to one of my customer, installed every update and security suite whitout any issue. She came back complaining that her computer won't connect to the internet. Here's my problem. If i connect any computer to her modem, it will work, her computer won't; if i connect the computer to another modem it won't work neither, any other computer will. So the only way to make the computer connect to the internet is by connecting it through a router or a simple switch, a direct connection to both modem i tried "Arris/RCA" won't work.

I already :
reset the computer modem a dozen of time
made sure the ip configuration was dynamic
changed the cable
tried to configure solide ip address with DNS and gateway address
tried to force windows to authenticate first without the Broadcast Flag then with the broadcast flag on failure
reinstalled the driver
CCleaner

Still get an "Unidentified network (Public Network)" with the message (No network connection / No internet connection)One or the other randomly and a 164.x.y.z address

It's now the second day i work on this issue and i won't find answer anywhere, i did everything that came to my mind and i don't know what else to do. The NIC LED do flash, so the NIC isn't the problem, and the modems both works with any other computer.

I'm lost help me please

 

[Emerald]

see if this helps

http://www.sevenforums.com/network-sharing/74556-enable-disable-tcp-auto-tuning.html

 

[hang-the-9]

It's not a good idea to be using a PC right off a modem anyway. She should be using a router for more security though the NAT and firewall.

 

[Phobophile]

We know it's working with a router, my client don't want it. A router won't solve the problem anyway, it just trick it...

 

[Phobophile]

So , i tried disabling the heuristics and autotuning level
also changed the ICMPRedirect to disabled. No change...

Is it possible that a NIC refuse to connect directly through a modem to avoid security issue ? Or that it just can't communicate with a modem because of a lack of a protocol or things like this. I'll search about a firmware update, keep you in touch !