Connection issue between fibre router and one PC

[#1]

Hi all,
I am having a connection problem with my fibre broadband router. The problem does not seem to be the internet connection itself, but between the router (Technicolor TG582n) and one particular Windows PC (running Windows XP SP3).
My fibre broadband was setup on 19th Sept, and had been working fine. Since 28th Sept, I having been getting a very intermittent connection to the router from the PC – it can’t connect to websites, or even the router settings login page (tries to connect, but sits there saying ‘waiting for’ whatever website I am trying to connect to). If I leave it long enough, eventually it will usually connect, but it can take half an hour or more. Sometimes it clears, and works fine for a period, then goes off again. If I manage to connect to a website and download a file or run a speedtest, the download speed seems fine.
I have tried in IE, Firefox and Chrome, and it is the same in all of them;
The issue seemed to coincide with me changing the wireless channel setting on the router from auto (which I tried as I was getting quite a weak wireless signal). I changed it back again once I noticed the issue, but this didn’t help (so may be a red herring).
I have restarted the modem and router, with no difference, and done a factory reset on the router. I have run virus/malware scans, with no issues found. I have tried connecting via ethernet cable and wifi, but it makes no difference.
Other devices connect wirelessly fine with no issues, and can access the internet with no connection or speed problems. It's only this one PC that is having the issue. If I start the PC in safe mode (with networking), the issue goes away, and it connects fine. It feels like it must be something to do with some dodgy settings on the PC, but I have no idea what.
Any suggestions as to what might be causing this?
Thanks,
Tony

[#2]

Which internet security package are you using and have you tried disabling it

[#3]

As Oldjim mentions, I would try and disable your internet security package and see if this makes a difference.
Have you changed anything else at all on your PC? Or any recent updates?

[#4]

Thanks for the quick responses.
I am using Norton Internet Security. I have tried disabling it, but it made no difference.
I installed Mozy online backup 8 days before this issue started. I uploaded about 100GB worth of files to that over 3 nights after installing it, with no issues. There have only been occasional small backups since then. I haven't tried uninstalling this yet, but have suspended it, which had no effect.
I haven't made any other changes that I can think of recently.
Tony

[#5]

I don't trust Norton's ability to 'let go' when supposedly disabled.  But it is very easy to uninstall and re-install; it might be better to completely uninstall it temporarily.

[#6]

I suggest trying msconfig and selectively disabling programs which run at startup
This explains it http://www.netsquirrel.com/msconfig/msconfig_xp.html

[#7]

If it's affecting both wired and wireless,  it could a corrupt IP stack.
The main question,  is the PC getting an IP address from router.
If it does, can the PC ping the router,  an external machine by IP (e.g. 212.159.6.9),  and an external machine by name  (e.g. google.com)

To reset the IP Stack, take a look at  How to reset Internet Protocol (TCP/IP)
This may also be useful How to determine and to recover from Winsock2 corruption

[#8]

Hi all,
Thanks very much for the suggestions, it is much appreciated. All of these look plausible and worth trying. I probably won't get time to do anything more until the weekend, but I will try some or all of these then, depending on how it goes.
Cheers,
Tony

[#9]

Hi all,
Just to update on how it is going. My PC's connection seemed to spontaneously come good at the weekend, and I had no issues. I have used MSCONFIG to stop a lot of unnecessary things running on startup, as that seemed a good idea anyway.  I shall keep an eye on how it goes.
Thanks for all the suggestions.
Tony