Dear Karthik,
Check SAPOSCOL service?
http://wiki.scn.sap.com/wiki/display/ABAP/No+History+Data+in+OS07N+or+ST06
Note 336120 - ST06/OS06: No data for 'recent days'
Note 977475 - ST06, OS07: No history data for different servers
If you are on Windows, you might also want to check the following:
Note 688131 - Windows: missing data in ST06/OS06
Regards,
V Srinivasan