One more thing.. Which operating system u uses on ur pc?

m usin' windows vista sp1

There r few thing if u can try...

Check in device manager whether all hardware and its driver working properly...
Check Is there any virus activity.. Run Windows Malicious Software Removal tool.. (x86 - x64 depeding on ur system)

Run ur System with minimum Hardware.. Keyborad, mouse and try to run it...if problem persist then test whether RAM is running ok.. Check for RAM if u can put another PC ram into ur infected PC... Check whther all the RAM are of same make and Mhz...

my rams are in gud condition.. i hv figured it out itz smps prob.. thnx 4 ur help..

My Suggestion- Never try the Malicious Software Tool Removal if you have a Pirated Version. Also, if its an illegal one I suggest not to install this software.