Windows XP Pro Browser STOPS

[wayshi]

My windows xp pro broswers both work ok for about 5 minutes and then they just can't find a page and time out trying to find a page ( internet Explorer and Fire Fox Browsers ) but if you reboot the PC the browsers work OK again but again only for about 5 minutes.
I've shut the windows firewall off and I have AVG anti-virus running but the problem is still there.
I will appreciate any help as I've talked to 2 help lines and all I get is " never heard of that ".
ThankYou

[guestolo]

Just to ensure it's not viral/spyware related
From my signature below, download and save too a permanent folder of it's own onto your harddrive
Hijackthis 1.99.1
Open Hijackthis.exe

Do a "SCAN and Save a Log file"
A log will open in Notepad
Copy and paste the WHOLE contents of the log  here... Don't try and fix anything yet----It is all important