These Steps should help you:-
1) Verify the External IP address on the Internet facing Interface
2) Verify the Default Gateway and next hop IP
3) Ping Next Hop and Any Internet IP from the ASA device using PING command(ping <ip address>)
4) Check the Outbound NAT on the ASA device.
For 8.2 and below:-
nat (inside) 1 0 0
global (outside) 1 interface
For 8.3 and above:-
object network obj-any
subnet 0 0
nat (inside,outside) dynamic interface
NOTE:- This can vary as per your requirement.
5) If all the above steps are good , post this output from the ASA device:-
packet input inside tcp <Any Internal IP> 3456 4.2.2.2 80 det
NOTE:- I assume Inside as your Internal Subnet interface and outside as your interface facing interface.
Thanks and Regards,
Vibhor Amrodia