Problem with mobo A8VE-Deluxe

Hi all,

I have a new mobo installed asus A8VE-Deluxe with a AMD xp64 3000 CPU
1gb of ram and a Sapphire ATI X700Pro 256MB DVI PCI-EX and Win XP
with all updates and SP2.
I have installed the VIA 4 in 1 drivers and in system he says that
all the hardware is installed properly. so no problems he says.
Every time after about 15 minutes, sometimes 30 minutes my pc is freezing
and all i can do is a hard reset and everything is working well again for 15 min.
All temperatures are fine.
I have no idea enymore what to do.
Is there anyone who knows this problem??
Please i need help. Thanks in advance for all the help.
(I hope my english is oke cause i am from Holland)