Try this from Arjun SV:
Turn off ur pc remove the cmos battery first, then short it by the help of a screw driver(u can see a silver metal with positive and negative, short them)
Then clean ur ram(remember u must very careful while inserting ram)
Then switch on ur computer a black screen asking Cmos time and so and so automatically it moves to ur desktop screen after that by turning off again u can insert cmos battery and on ur PC again and adjust the time...when desktop screen appears again