Cannot Browse Web Pages but can Ping Successfully

My SBS server has begun to misbehave (well I assume it's the server as BT - who provide the ADSL connection  - claim everything is working at their end). The problem is in relation to web pages. Neither at the server nor client level can anyone access a web page but VPN, RWW, Skype, TS, etc all work great - you simply cannot receive a web page on any machine.
 
I've checked to ensure that I can ping an address from the command prompt and this works fine (I can ping www.google.com for example and it returns an IP address) but when I enter either the IP address of the web address into IE7 then I get a Page Cannot Be Displayed error. This has only started this morning and nothing has chnaged at the server level (I've not been on this machine for a few days now).
 
Having spoken to BT they claim the problem is server related as there is no problems on the DSL line so I did some hunting and came across similar scenarios elsewhere but it seems such a wide ranging problem I was wondering what others thoughts are.
 
The articles I've found in relation to this are:
How to reset "Internet Protocol (TCP/IP)" in Windows Server 2003 - http://support.microsoft.com/kb/317518/
Winsock Problem - http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Windows/XP/Q_20799216.html?sfQueryTermInfo=1+can+cannot+displai+page+ping+web#a9756715 (more XP I think rather than SBS)
 
Could it be caused by spyware? There is no anti spyware on the server but no one has been using it directly other than myself and it's not used to view web pages as such.
 
I've also noted that the Primary DNS on the DSL box has changed since I configured CEICW so I wasn't sure if this was also playing into this (it would seem strange to me as I can ping an address from the command prompt).
 
Any ideas greatly appreciated...hopefully before I pull my hair out!
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Steven O'NeillSolutions ArchitectAsked:
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Jeffrey Kane - TechSoEasyConnect With a Mentor Principal ConsultantCommented:
If your ISP's primary DNS changed since you first ran the CEICW, then run it again to update it.

Pinging is not the same as sending an HTTP "GET" request... they'll take different routes, so it's not a good measure necessarily.

The other thing that can cause this is MTU settings.  See my answer in this question for info on that:  http:Q_21963681.html

Jeff
TechSoEasy
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Steven O'NeillSolutions ArchitectAuthor Commented:
I've determined that I appear to be able to browse to sites like the following:

http://inside.c-spanarchives.org:8080/cspan/schedule.csp

https://www.nwolb.com/

Neither site use port 80 so I'm assuming that outbound port 80 is being blocked in some way. I'm not using ISA on this server and the only firewall in place is the built in NAT/Basic Firewall and the Firewall within the BT Router (and this Router has been thru multiple power cycles today).

Any other ideas?
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Steven O'NeillSolutions ArchitectAuthor Commented:
The solution to this problem is quite easy (when you know how!). The firmware had changed on the router from the last time I monitored it (I mentioned this to BT as a potential problem which they disregarded). However on closer inspection the firmware appears to have reset a number of items to their default settings including some of the firewall settings. The main one being a monitor called Excessive Session Detection. When this is on then it looks to see if there are excessive session (obviously) but as this user is a heavy Skype and P2P user then they get a false positive here as these programs also appear to look like excessive sessions on the network. Simply turning this setting back off (it was already until the firmware update) sorted everything out.

Thankfully I keep a screen shot of all settings of all devices I setup on a network and on closer inspection was able to determine this. Not happy with BT for doing this to a router but as it's theirs then I really cannot complain too much.

Thanx for all advice guys...gives me some food for thought in the future.
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