I have 3 identical Dell Vostro 200 slim desktop machines running Vista on the same wifi network. One of the machines has developed an issue where its wifi connection is very slow; webpage loading times are easily a factor of 10 slower than a few weeks ago.
For example: loading thesimpsons.com takes <20s on machines A and B, but machine C still hasn't completed the loading after 2mins.
I've checked the settings for the built-in wifi card and they're again identical.
Viewing the network usage while a browser open shows the download happening, and closing the browser immediately stops any download traffic - so there's nothing on the machine leeching bandwidth.
None of the machines have QoS enabled or even installed.
Vista notes the card as a Broadcom 802.11g Network Adapter "BCM43XG_NT60".
There's no previous driver to roll back, and there are no new drivers from windows update.
What would be the next step to debug this issue?
I'd first check for the usual suspects...if all three are identical (software versions, treatment by users, etc.)...reseat cards that can be reseated. Run disk checks with a diagnostic program. See if the slow system speeds up when connected to a wired connection instead of wireless.
Install Spybot Search and Destroy to search for malware, update your antivirus, see if they find anything.
Chkdsk it, see if that reports anything, along with the built-in Dell diagnostics.
Swap parts among the three to see if that narrows down the problem.
Last resort find a cheap wireless card and put that in as a second adapter and see if it works fine. If it speeds up then you may have a faulty wireless card that Dell would have to replace.
First of all, have you tried to update you adaptor drivers? And also, you forgot to tell us what are the brand and the model of you wireless adaptor in your laptop. Dell can come with Intel or Dell (wich are generaly broadcom chips) wireless adaptor..
And, this is maybe more a question for SuperUser (www.superuser.com).
Considering that you appear to have three identical machines, I doubt Vista is the cause of your issue.
It sounds like the problem lies in a hardware failure, maybe the card is defective, or a software issue, it's possible you have a virus or some type of software conflict.
Since you have three of the same computer, the easiest way to check for a hardware problem would probably be to just swap the wifi card for one from one of the other laptops. If the one that was having a problem starts working better and the one that wasn't before starts having problems then you know it is a problem with the card. If there is no change after swapping the cards, then you almost certainly have a software problem.
Checking for software issues may be a bit trickier. Check for malware on the computer if you haven't already. Definitely check for updated drivers as the above answer recommends. In the end, the best solution may just be to back up and restore the operating system.
If the laptops are on battery then i would check the power settings as Vista's settings for power control can be a nightmare for your speed (power consumption over speed = battery life). I was being disconnected all the time on my laptop and i found that the power management for the card was all over the place the minute i went to battery. Failing that if they are all plugged in i cant see what could be the difference.
Are the DNS settings the same for the adapters on each PC? Sometimes a rogue entry for DNS can slow things down. Perhaps trying a public DNS, or if on a network, insuring the internal DNS server is specified might help.
What about clearing the cache on the browser as well. A good scrubbing with CCleaner can do wonders as well.
Mabye if you moved machine C on to a different wireless channel and/or frequency band range?