ORA-12170 error occurred

I am trying to connect oracle 10g db through TOAD from another machine. But failed, got error as

ORA-12170 connection timeout occurred.

Please help me.

There are a couple of possible reasons for this error:

• DNS resolution problems (try nslookup <hostname> to verify DNS resolution is working)
• the listener might be running on another port (standard is 1521, check with your DBA if necessary)
• there might be a firewall in between that blocks you from accessing the database (does connecting locally on the server work? Can you connect from another machine?)
• the listener on the database might not be running (try connecting from your machine with sqlplus)