Cable-modem gurus, I need your help... [Solved]

[AzureFan]

(Complete system specs below)
I am trying to solve a problem I have with my cable-modem connection at home. The problem i'm facing is intermittant and it's been happening for two months now. At times, everything works fine, web browsing is fine, beautifull pings... But most of the time it just completely refuses to work... It's like there's no communication between my ethernet card and the modem. When the computer boots, i have 169.254.127.104 as my IP address (autoconfiguration) and executing a ipconfig /renew has no effect at all... At some other times, while working on the Internet, it would just slow down and eventually cease working... When I try a ping in these circumstances (for example to www.yahoo.com), I get anything between 1% to 100% packet loss....


I called my ISP (Videotron) multiple times, they sent in tech support guys, checked signal levels on the cables outside, etc... and the problem was still not obvious (they didn't check the computer itself)... They suggested in the end that the problem was with my PC. Here's what I have tried so far:

- Switching NICs (different PCI slots and different brands -- D-Link and SMC);
- Removing all other PCI cards;
- Uninstalling/reinstalling TCP/IP drivers;
- Installing a different OS (Windows 98 SE) on a newly formatted hard drive;
- Resetting the modem by unplugging the power cable (Note: When reconnecting after about ten minutes, everything works again but then the same problem comes back after a while);
- Trying different RJ45 cables;
- Visually inspect the cables next to house (no apparent damage...)

One thing I will try next is to connect a different system if i can get my hands on a different one...

I never had any problems in the past with the same computer. It is very stable and it has no hardware conflicts. I should also mention that my ISP tried pinging the modem itself a few times with 0 packet loss, so they assumed the modem is fine.

So any suggestions on what could be the problem or what could be tried, as i'm completely out of ideas and almost desperate, would be much appreciated.

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System Specs:
- Socket A ASUS A7V motherboard with the VIA KT133 chipset
- 900 Mhz Athlon CPU
- 384 Mb PC133 Mushkin RAM
- 300 Watt Enhance power supply
- Asus V7700 Deluxe Geforce2 GTS video card
- 30 Gb Quantum Fireball LM30 hard drive
- Creative Sound Blaster Live! sound card
- ESS 56K fax modem
- D-Link DFE-530TX or SMC EZ Card 10 (SMC1208) NIC
- Samsung SCM-110R InfoRanger cable-modem
- DVD and CDRW
- USB Keyboard and mouse

OS:
- Windows 2000 Professional SP3