From Oracle FAQ
ORA-12170: TNS:Connect timeout occurred
What causes this error?
An ORA-12710 error occurs when SQL*Net cannot connect to its destination. Common causes are firewalls blocking connections and network routing errors.
How to fix it
Open firewall to allow SQL*Net connections through
Open firewall settings and ensure the listener port is not blocked.
For example, on a Windows system, navigate to Control Panel-> Security Center-> Windows Firewall-> Exceptions. Click on Add port and add TCP port 1521 or whatever port the listener is running on (see listener.ora).
Troubleshoot networking between two systems
Use utilities like ping, tnsping, netstat and traceroute to see if the two systems are connected on the network.