I think I have figured out what the problem is -it's the temperature. Planning to clean the air ducts, reapply thermal compound and buy a laptop cooling pad. Will let you know how it goes after all that
Hi Mike et all, Finally done with the laptop cleaning and thermal paste reapplying . As in your photo, my laptop also had $~%t load of dust, only double the quantity!! Applied Arctic Silver 5 compound and now 3Dmark11 is promptly back to normal. I reckon your suggestion of cleaning the laptop was what helped me. Because of high density dust accumulated in the heat sink, the chassis temp was crossing 95C. This extreme heat was somehow throttling graphics card performance. After cleaning the laptop, chassis temp wont cross 80C under full load. So is the case with processor. Here's the latest 3DMark11 score - http://www.3dmark.com/3dm11/8214027
Thanks a lot for your help. The forum has always been very helpful thanks to gentlemen like you.