Hi syedtouseef,
Thanks for reaching out with your query. This could also be an issue with the motherboard. It normally happens when the mother board does not detect the adapter anymore. However you can check the status of the adapter in the BIOS set up to confirm.
Start the system and hit F2 on the Dell logo screen. In the BIOS set up, check if the adapter is listed as 90w. If the adapter shows 'none' or 'unknown device installed', then we can be sure that the issue is with the motherboard and needs replacement. Also check if a good known adapter works fine.
For more information on Adapter and battery charging issues, check this link: http://dell.to/1bFIYzs