Laptop gives HTTP 400 error

Hi

I've bought a new laptop with windows vista about a month ago, and since last week ive been getting alot of HTTP 400 errors from alot of websites.
ebay, yahoo mail, alot more.

I know it's not my network/router because i get the same errors on other networks, and it dosen't happen on my main PC.

I get the same error in firefox and IE.

At first it just used to happen sometimes on ebay, but it's sort of, grown?

any idea wht it could be?

Many thanks,
John

EDIT - I am using the virgin media firewall and antivirus suite which my aunt also uses without any issues on her XP laptop.
My PC is running Zone Alarm / AVG with Vista

 

Sorry i didnt make that clear


My laptop is running a virgin media firewall and antivirus software suite for protection, nothing else.

its my PC that is running zone alarm and AVG. without the virgin media software.


I am not running 2 firewalls on the same system. it's just my laptop thats bothering me

 

thanks, but still no luck.

any other suggestions?

btw, its not all websites that dont work. Just the ones i use the most haha

 

Im still having no luck.

i've tried completely removing the security suite. re-installing the browsers. taking all the security levels down.

and nothing..

 

sorry, i forgot to mention that i have also tried out the suggested sollutions