ISA 2006 sp1 - Internet stop working for few min. & start by it self

Dear All,

I am usign the ISA 2006 sp1 ,

i am having problem like , the internet stop working for few min. & start again by it self, it was having the problem before with MAC Laptops, now it happen with the windows pc also,

 i tested my wifi connection , lan, Firewalll connectivity everything is fine, while stop browsing the it can ping the ISA & other device, i can open the Itranet sites also, but the problem remain the same, i do't get any logs on the ISA or WIFI AP , i do not understand how it is

anybody having any clue