if you could post pix interface stats we could see if there are any errors.

telnet to pix and issue these two commands bellow, strip out any public IP address information.

show interface ethernet0

show interface ethernet1

make sure the pix ethernet connections are hard coded on both ends, e.g if your pix inside interface connects to a switch make sure the switport is also 100/full duplex hard coded, same for your outside interface.

HTH

Jorge