Strange Internet-Related Problem - HELP!!

Got a stumper here. I recently purchased the following:
ECS K7S5A Pro Mainboard
Athlon XP 2400+ CPU
Seagate ATA-V 120GB HDD

Other system information which may be pertinent:
3Com 10/100 ethernet adapter (using WinXP drivers)
Onboard NIC (Disabled in BIOS)
Sound Blaster Audigy (Latest drivers)
WinXP Pro, with SP1 and all critical updates

I had a very serious problem (documented here ) which may have been caused by my motherboard or IDE cable, or maybe by me - because looking back, I may have accidentally disabled the Remote Procedude Call service in WinXP. Don't know if that would cause the issue I had, but I know the service can't be disabled. I updated my BIOS, switched IDE cables, and tried to be a little smarter about the order in which I installed my drivers - and so far, the new WinXP installation seems to be fine.

However, once I got my programs installed, I moved the computer into my bedroom and almost immediately started getting a problem - I periodically lose Internet connectivity until I reboot the computer. The weird thing is, the extent of the connectivity loss varies, and how long it takes for me to lose connectivity is totally random. When the problem manifests itself, generally I have no connectivity, can't ping, can't make a DNS call, can't traceroute. However, there are some times when performance is just severely degraded. For instance, maybe I'll be able to make a DNS call, but not ping an IP address, or I'll be able to traceroute, but 80% of the hops will time out (and the rest will be very long). When I reboot the computer, everything's fine.

This does not seem to be a network issue, because:
- I cannot resolve the issue by power cycling my cable modem or network hub
- I cannot complete an ipconfig /release, ipconfig /renew operation
- The issue is always resolved, for anywhere from 1 to 60+ minutes, by rebooting my computer
- The issue does not seem to resolve itself on its own. I have to reboot the computer to regain connectivity.

Other symptoms I have found:
- Sometimes my computer's sound will be screwed up (very crackly) until I reboot the computer, other times, it's fine. So, I tried listening to music on my stereo instead, and not using the computer for sound. This did not resolve the issue.
- Sometimes my USB hub will turn off and back on, other times, not. So, I tried connecting my mouse directly to a USB port and removing the hub. This did not resolve the issue.
- When these do happen, they happen in conjunction with the connectivity loss.

Here's what I've done to troubleshoot, so far:
- I noticed that the Power/Aux temperature reported in Sandra is high. I don't know if that actually comes from the power supply temperature sensor or something else, but it's reporting 48 C when I'm used to seeing it room temperature. I wondered if I might be overloading or overheating my power supply (Enermax Whisper 350W, no problems previously, used to seeing every rail above the voltage level they're supposed to be, but now they're just slightly lower). I went from a PIII-Tualatin 1200MHz to the Athlon XP, and went from two hard drives to one, so it seems like the load should even out, or even be lower. I dunno. In any case, I turned all of my fans up to top speed, and that didn't resolve the issue. I figure, anyway, that if this is a PSU overload/overheat, then rebooting shouldn't fix it.
- Although this is a brand new Windows installation, I did scan with Norton using fully updated virus defs, and didn't find anything.
- Spybot Search & Destroy reported nothing, other than the usual tracking cookies.
- I installed Zone Alarm Pro (usually, I don't like to use a firewall so I keep it off the computer), and found that nobody seems to be hacking me.
- I ran a full port scan on my computer for trojans, and the computer does not appear to be listening on any port. The smaller port scan at grc.com also came back saying all ports were stealthed. The NetBIOS port on my machine is also stealthed.

Things I haven't tried yet:
- Updating my USB controller drivers. I just let Windows XP discover everything this time around.
- Using my onboard NIC, or moving my card to a different PCI slot.
- Giving it time to see if it might be a network issue (which I don't think is likely).
- Trying a different computer (Haven't had enough time to troubleshoot; issue just began a few hours ago).

So, is this enough information? Any thoughts or suggestions would really be appreciated, here.

A few quick things to try in regard to your network issues:

1) Try a different cable. Sometimes a flaky cable can manifest itself in connections that drop off like you describe. That wouldn't explain why it works when you reboot, but if you've got a spare cable, it's a quick test so it's worth a shot. 2) Try updating your network card's drivers. 3) Try reseating the 3Com network card and/or moving it to another slot. 4) Try the onboard NIC instead. (You can have both NICs enabled at the same time.) Besides, the difference in performance between your onboard NIC and the 3Com would probably be imperceptible if there's any difference at all.

The USB & sound issues coinciding with the loss of network connectivity seem pretty strange. From what I've read, it seems like when the network card goes on the fritz, it takes other stuff out with it. I'd try getting the network issue straightened out first and see if that has any effect on these.

Hm. Well, I tried the onboard ethernet. Guess I should have done that first because sure enough, more than an hour in, I've had no problems. Guess I'll try reseating the card in a different PCI slot when I have a chance, and see if that resolves the issue. Thanks for the posts, SkyDog. Never in my life have I experienced so many random issues with the same computer.