Massive internet trouble

I'm running an Acer Travelmate 2480 with Windows XP, as well as a more modern desktop Compaq running Windows Vista. Both connect through a Comtrend ADSL2 wireless router/modem, with the desktop hardwired directly into the router.

Two nights ago, I started noticing issues with websites that were off-and-on inaccessible. Thinking that cycling the modem/router would help, I did so. No dice, it didn't even put a dent in the problem. I then cleared both my browser cache and my DNS cache on the laptop, as both computers were having the same problem. Still no help.

The problem sites are random. One minute they work, then poof! No access for between ten minutes and an hour. I maintain a constant connection to the AIM service, which usually alerts me to problems with the connection itself; it hasn't so much as blinked this entire time, aside from the ad on the main program window. And while there are some that are more consistently problematic than others (Yahoo mail, I'm looking at you), there are some that make absolutely no sense whatsoever (down for everyone or just me?, for instance, would let me load the initial page but not run a search, even after clearing cache.) Other trouble sites include, but are not limited to: My personal LJ (but not anyone else I checked), LJ communities in general (I can't even load http://community.livejournal.com half the time, don't even get an error page aside from 'Server not found'), various image hosting sites, World of Warcraft's community page, and Eyrie Productions. And yes, I have asked other people to check the mentioned sites when I was having trouble; they reported that the pages loaded perfectly for them.

I've tried checking all of the above sites with and without an active firewall, with no discernible change. Windows Firewall and PC Tools Firewall Plus are both currently disabled on my laptop; after posting this, I intend to turn the later back on.

I've contacted my service provider, and they assure me they've placed no blocks on my service. I've run full virus and malware scans on both machines, all of which turned up negative. I am well and truly stumped by this one, guys. Any help would be greatly appreciated.

 

Update:

Flushing the DNS cache (via command prompt) as well as the browser cache seems to resolve the issue, at least for a little while. Unfortunately, it's a temp fix as the problem returns within thirty minutes, and no virus or malware scan I have run to date has caught anything bigger than tracking cookies.

My ISP's tech department is woefully inadequate; beyond the command prompt DNS flush tip, they haven't been able to tell me anything beyond the fact that it's apparently not on their end.

I'll try to keep information coming as I get it, but at this rate, I may end up having to partition the drive and install a backup OS to see if the fresh install helps.

 

...okay, I spoke too soon. The aforementioned method does -not- work every time.

 

Just to be clear, is it just the one laptop that you are having problems with, or both computers? The way I'm reading it, it's your XP laptop that you're having the issues with.

 

Both computers are having the same problem. I speak about the laptop more because it's the one I work with more - it's mine. The desktop is more of a community machine, as it were.

Is it possible that problems on one machine could be affecting both?

 

I doubt that a problem on one PC is causing issues with the other unless it's virus/malware infections traveling through your network-which I don't think is happening. Since it's both computers having problems, it does point to network issues versus software. If you are sure your connection is working, it might be DNS issues. I'm wondering if your router may be having issues forwarding the DNS requests.

To test this, when you are down, go to a command prompt (Start, Run, cmd (Enter)) and type "ping 208.67.222.222" without the quotes and press enter. If you get replies back, your internet connection is working and it is DNS related. You can further test this by replacing the 208.67.222.222 with a web sight ie www.google.com.

Instead of replacing your modem/router, you can just manually enter the DNS servers into you TCP/IP settings of other your ISP's-which they should be able to provide. Or I recommend using OpenDNS servers (208.67.222.222, 208.67.222.220).

Here's how to do this.
http://support.microsoft.com/kb/305553

Click Start, click Control Panel, click Network and Internet Connections, and then click Network Connections.

Right-click the network connection that you want to configure, and then click Properties.

On the General tab (for a local area connection), or the Networking tab (for all other connections), click Internet Protocol (TCP/IP), and then click Properties.

If you want to obtain DNS server addresses from a DHCP server, click Obtain DNS server address automatically.

If you want to manually configure DNS server addresses, click Use the following DNS server addresses, and then type the preferred DNS server and alternate DNS server IP addresses in the Preferred DNS server and Alternate DNS server boxes.

 

I've been pinging and tracerouting through the command prompt since the problems started happening. Ping goes through fine, and I typically do two or three in a row just to make sure, to different sites.

It occurred to me earlier that I had not run the suite of spyware/malware/virus detection software on the desktop. Having run it and encountered a couple different infections, I'm waiting to see if things have cleared up. Will post further information as I get it (along with the names of the infections).

 

Okay, I think I've got this one licked. Either cleaning up the desktop fixed the problem, or my ISP got their act together about the same time I finished scanning it, because I haven't had a problem since. The infections were Vundo and trojan downloaders; I'm not sure offhand which ones, specifically, but there were at least two different trojans.