One by one u have to check:
1. Check for virus / malware by a solid antivirus
2. Check your firewall rules and settings
3. It might be a lock or server resources (CPU, RAM)
4. Pathing hang – Make sure that your Oracle environment variables are properly set
5. External hang – The network being down,
6. Listener down/hanging – Start by checking the listener (check lsnrctl stat)
7. RAM shortage hang – Over allocation of server resources, usually RAM, whereby there is not
enough RAM to spawn another connection to Oracle.
If above r okay then u may reinstall the same !
Sorry! I missed it, if possible check for virus also