If you were using magento 1.4 and above, please follow the instructions

Goto app/etc/local.xml

Find the following lines

<host><![CDATA[localhost]]></host>
<username><![CDATA[root]]></username>
<password><![CDATA[stability]]></password>
<dbname><![CDATA[pe_vivek]]></dbname>
<active>1</active>

I guess you can easily modify now the username and other details
Leave out your comments if this doesn’t work