Thank for your reply, I bought my N900 yesterday from Nokia Care and its working fine now, also i found that there was no change in the phone software as he told me because all the files, programs, theme customizations, power kernel, cssu and overclocking is all there, the only thing i found changed is that, its now working perfectly well same as before and the keyboard slider is tight as a new phone, the only defect i found is theres a slight gap between slider keyboard and screen which is causing little blurry point on right side of the screen (only when pressed the screen to close the gap), like something is pushing from bottom, anyway i think the phone locked by itself when it became too hot, and the man at nokia care just opened the phone and unlocked it (i believe). I really need to know what really happened but its a mystery case yet unsolved.

Edit: oops.. jus now i found my camera is not working properly, the photos are horribly blurred, i think the camera sensor is damaged probably by that stupid Nokia care person,