Internet issues Windows 7

Hi,

I have installed Windwos 7 on 2 seperate computers a Laptop and a Desktop... My problem is... After about 4 days being logged into the computers the internet just stops working, if i do a CMD and ping an address it works!! but I get the connection error in IE and any other net application, the only way to make the internet work again is to log off and then to log back on again...
It does the same thing on both computers funny thing is that i installed Win7 a day apart on both so the Laptop goes down and the next day the Desktop does it.
Its not a net connectivity issue as every other device on the wireless network works still...

Any advice?

Hi "The_Prophecy" I have done this on both systems already... the lappy is a HP and the desktop is a home built... HP all updated from the HP site and the desktop updated using the manufacturers website...
The network still works perfectly, its just nothing will work with internet... MSN sometimes will still work even when its saying their is no net in IE, have also tried using Firefox and Safari but they have the same result.