dead arduino?

my arduino will not talk with my computer win i plug it in

Turn everyone on to the particulars: which Arduino, your computer, etc.

uno mac usb

also i was looking and i will use a isp

"...will not talk ..." ??
any error messages, further details

Which model ?
If UNO has it talk before ? or is this a new problem ?

If he never talk perhaps you have a bugged Atmega8 firmware, upgrade it.
It is a well known problem particulary on Linux, Mac and Win7 64bits.