firefox not resolving dns

[#1]

I recently posted about a pc that woulnd not boot. this is now fixed, but the system is not good. firefox refuses to resolve dns names, but will find internet addresses via IP. IE works with most sites, but is very slow with some. windows update refuses to load. AVG will not complete its updates at all, I just keep being told to reboot. I have tried running a spyware scan with spybot ( updated OK!!), and nothing of note, and a virus scan comes up clean. I an resigned to a reformat and reinstall I suspect, but wondered if anyone could maybe help. I have done a system restore to 2 months ago, when system working ( or so I am lead to beleive), no change. I also set up another user, on the off chance it s corrupted profile, still nothing.
Any help appreciated.
Oh and also zonealarm refuses to install, something about a missing dll.

[#2]

Bring up a DOS box and type ipconfig /all and post the results.
Also what ADSL equipment do you use: router, ADSL modem etc and how do you connect to it: USB, Ethernet etc..
Try manually setting DNS in Windows to:
212.159.6.9 & 212.159.6.10
or try a non PlusNet setup like OpenDNS
208.67.220.220 & 208.67.222.222

[#3]

Thanks Peter.  The IPconfig looks OK.  I am using a router where the system is, but my brother in law, actually has a USB modem. Wouldnt have thought that would be a problem. Things have progressed a little. AVG now updating, after following some instructions from Grisoft. Zonealarm now installs, again after removing some files on instruction from Zonelabs. I manually completely uninstalled firefox, and ran a registry clean. Still the same issues with Internet access. Some sites work fine in firefox, others not at all, but some that do not work, work Ok when IP addressed, but I cannot browse to other pages within the site. I have tried using Open DNS servers, no change.  IE opens somw of the pages forefox wont, but a goole search will not run in both IE and firefox. I can download files fine, such as antivirus updates, but access to windows update is not possible. Also outlook express downloads and sends E-Mails fine. I am absolutely stumped. Updated Spybot finds nothing of note, and a virus scan turns up empty. I think its an infection of some kind or a funny DNS issue ( unlikely I think), or more likely a windows corruption issue. I have used the Winsock fix.  Anyone any ideas before I just cut my losses and reinstall windows?

[#4]

Can't think of anything other than some form of corruption in the windows install.
Do you have the original MS install media to allow you to do a repair install?
If you are using IE7, try uninstalling then reinstalling although it will need access to the net to get the update again so maybe that's not possible.
Have you tried resetting both IE and firefox to their default settings?

[#5]

Thanks Peter.  yes I have the XP install disk, so I presume I can attempt a repair install, and hopefully that may work. Easier than a full reinstall.  Using IE6, and I have reset both IE and Firefox to defaults. Even tried safari, and that dont work either.  Would a repair install, get rid of spyware/malware??  or is it just easier to reformatt and reinstall.

[#6]

If you decide to re-install I would say it is worth deleting disk partitions and setting them up again just in case you have something nasty sat on the boot sector that might survive a format.

[#7]

Thought I would let you guys know, fixed it. Had a brainstorm to completely remove and uninstall the LAN adapter, and reinstall. Seemed to work a treat.
Thanks for your help.
Chris

[#8]

we seem to be having some DNS resolving problems with the old Force 9 DNS servers, looks like it's fixed now, could have been that 

[#9]

Quote from: penfold

Thought I would let you guys know, fixed it. Had a brainstorm to completely remove and uninstall the LAN adapter, and reinstall. Seemed to work a treat. Thanks for your help. Chris

Don't ya just love these 'logical' solutions to our problems, man computers never behave logically... must be the fault of the humans involved in all the processes !