Hi Challoju Ravi,
As Graham Slater updated in above, blog for startup troubleshooting will help to identify where the proble is
Please check as above and attach the relevant log file here
You can also check memory parameters with sappfpar
logon as <SID>adm and run sappfpar check pf=<instnace_profile>
You will get more details about this here,
http://help.sap.com/SAPhelp_nw70/helpdata/en/66/380fb7d43d11d188bd0000e83539c3/content.htm
Best regards,
Praveen