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The 12541 simply says you don't have a valid connection. &nbsp;From the looks of things I'd start with the listener process. &nbsp;Your listener log and your alert log I presume you've already checked?<br />
&nbsp;<br />

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The 12541 simply says you don't have a valid connection.  From the looks of things I'd start with the listener process.  Your listener log and your alert log I presume you've already checked?
 


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Where is the listener / alert log ?<br />
<br />

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alert.log is traditionally found in the BDUMP directory under ORACLE_HOME, for example /ora01/app/oracle/product/<wbr />10.2.0/db_<wbr />1/admin/bd<wbr />ump. &nbsp;Your actual results may differ. :)<br />
The listener.log is likewise under the ORACLE_HOME, as in .../network/admin .<br />
&nbsp;<br />

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alert.log is traditionally found in the BDUMP directory under ORACLE_HOME, for example /ora01/app/oracle/product/10.2.0/db_1/admin/bdump.  Your actual results may differ. :)
The listener.log is likewise under the ORACLE_HOME, as in .../network/admin .
 


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I install the Oracle 10 after that I create database called Test_Db and the SID is TestDb<br />
<br />
But when I run the Enterprise Manager I get Database Instance is down and Listener<br />
<br />
See the picture <br />
<a href="https://filedb.experts-exchange.com/incoming/2008/11_w46/77782/OEM.JPG" target="_blank" class="file-inline" title="Enterprise Manager is not able to connect to the database instance (109 KB)"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M67.508 468.467c-58.005-58.013-58.016-151.92 0-209.943l225.011-225.04c44.643-44.645 117.279-44.645 161.92 0 44.743 44.749 44.753 117.186 0 161.944l-189.465 189.49c-31.41 31.413-82.518 31.412-113.926.001-31.479-31.482-31.49-82.453 0-113.944L311.51 110.491c4.687-4.687 12.286-4.687 16.972 0l16.967 16.971c4.685 4.686 4.685 12.283 0 16.969L184.983 304.917c-12.724 12.724-12.73 33.328 0 46.058 12.696 12.697 33.356 12.699 46.054-.001l189.465-189.489c25.987-25.989 25.994-68.06.001-94.056-25.931-25.934-68.119-25.932-94.049 0l-225.01 225.039c-39.249 39.252-39.258 102.795-.001 142.057 39.285 39.29 102.885 39.287 142.162-.028A739446.174 739446.174 0 0 1 439.497 238.49c4.686-4.687 12.282-4.684 16.969.004l16.967 16.971c4.685 4.686 4.689 12.279.004 16.965a755654.128 755654.128 0 0 0-195.881 195.996c-58.034 58.092-152.004 58.093-210.048.041z"/></svg>OEM.JPG</a>
</div>
</div>


Enterprise Manager is not able to connect to the database instance

OEM.JPG

I install the Oracle 10 after that I create database called Test_Db and the SID is TestDb

But when I run the Enterprise Manager I get Database Instance is down and Listener

See the picture 

Oracle is an object-relational database management system. It supports a large number of languages and application development frameworks. Its primary languages are SQL, PL/SQL and Java, but it also includes support for C and C++. Oracle also has its own enterprise modules and application server software.