SREDDY is 100% right. I alredy posted the solution for that, still not working?? see, if your OS is linux/Unix, just type at $ prompt : oerr ORA -
eg:
$oerr ORA 01658

This gives you the action to be taken.
seems, The momnet you are struck, just posting the error in the forum, seeking help from others. I suggest you to go for reading in OTN and some other sites like tahiti.com, google search, and then still won't work, then come here.ok.
Hope this may help you,

Thanks