Did you check:
- if squid is actually running?
- if it is accessible from localhost?
- if squid.conf contains both of these lines:
acl mynet src 192.168.0.0/255.255.0.0
http_access allow mynet
(in this example the acl allows access from the 192.168.0.0/24 IP range)
- if the above lines are at the correct place, i.e. mynet is not denied by a preceding rule?