OEM shoots VTK-1000 error if OMS service is not started or OEM repository does't exist. 
so in control panel/services start the services for OEM, Inteligent agent etc and make it auotmatic. 
make sure u first
start the concerned database ( for repository)
start the intellligent agents of all concerned nodes.
then, start OEM.(the databases should be started before OEM services 

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but 
[i]oracle.sysman.emSDK.client.omsClient. ClientException[/i]
is a different issue.
verify that you can telnet into port 3339 from your client machines. If you cannot, verify 
that the EM weblistener is accepting connections (try to connect to EM on port 3339 locally). If it doesn't work, then
the EM Web Listener isn't running or isn't properly configured. 
else
is there any firewall ???
look into logs and post more details error messages.

replace hostname with IP and try again.
else
1. 
Add a line to the TNS_ADMIN TNSNAMES.ORA file that is
pointed at by TNS_ADMIN environment parameter, to
include the file used by OEM. 
This entry should look like an "ifile" entry on one line by itself, "ifile=<file spec>" 

Example: IFILE=C:orantnet80admintnsnames.ora 

2) Alternatively, create a small instance with ORCL as
sid. Use this as a repository for the OMS. If OEM 
cannot find tnsnames.ora, it will default to ORCL