Hi.

I recently formatted my hard drive and re-installed Windows 2000 + Service Pack 4 from scratch. I took great care in making sure every last setting and driver installation was correct.

As far as I can remember, I've been having this problem since I finished the installation, so I'm pretty sure that it's not from spyware or viruses. I recently did some scans anyways, and it didn't help.

Whenever I start up a game of mine called Worms Armageddon, just a few seconds after it switches to full-screen, my connection drops.

As far as I know, the game does not try to send or recieve any information on startup, as it just goes to the main menu.

A few seconds after this happens, the modem light flickers back on, as the connection software is set to automatically re-establish the connection if it drops.

After the connection is re-established, I am able to log into the game's online lobby. The connection then stays until a match is started. When that happens, the resolution changes, the game loads, and the connection drops/reestablishes again. The connection also drops whenever I exit a match back into the lobby, minimize the game, or quit the game completely.

I am not always able to continue after the modem light comes back on. Half of the time, I have to quit the game, exit the connection software, and start from scratch.

I have no other connection problems besides this. All of my browsing and file-sharing works fine.

My specs are:

ISP: MTS Allstream
Modem: Efficient Networks Speedstream 5200
Connection: ADSL via PPPoE @ 1.5 mbps downstream, 384 kbps upstream
Connection software: Efficient Networks Enternet 300 version 1.5c
CPU: Athlon XP 3200+ Barton Core @ 2.2 GHZ, never overclocked
RAM: 1GB Kingston HyperX DDR, never overclocked
Video card: XFX 6600GT
Motherboard: Asus A7N8X-E with nForce2 chipset
LAN: Onboard 10/100 Nvidia port

I built my computer myself, and I can assure you that all the connections are secure, all the BIOS settings are correct, and that the power supply and cooling are sufficient.

The problem seems to have fixed itself...

Hm...

And now it's back!

Examine the Events Log for errors that occur at that time. (Assumes Win2000 has that capability.)
Your description places the event close to the change in the video display. To me that suggests a conflict or corruption involving the video drivers. Additionally, testing RAM is easy to check out. Checking video RAM is harder if a diagnostic utility was not included with the graphics card.

There wasn't anything in the Events log, but I fixed the problem. Turns out that the nVidia site had told me to use outdated drivers. I got suspicious when dxdiag told me that one of the files wasn't digitally signed. I got the latest download, and with it, no more connection drop.

The problem is back again, but I finally 100% figured out what's going on. When my CRT monitor switches modes, it interferes with the modem. I tested this by starting the game with the modem on the floor, and in it's usual spot next to the monitor. Guess what happened?

I'll have to go and buy a longer ethernet cord to fix this. Weird, huh?