When i start My pc it automatically restered and there is no boot screen all MB is working good and its starts fan lite and everything.

I tried clearing bios but failed , replacing ram also failed.

I want to re installing bios .

please help me.

Ok, i think everyone here will need a lot more information like the make and model of your motherboard, what were the symptoms exactly and what did you do and how you did it.

If you provide no information, unless someone has a spare crystal ball to share with us, i don't think anyone will be able to help you efficiently.

As a generic advice, if it is a desktop computer, you could try removing all parts then add one by one ( begining with cpu then ram then video card if existing then hard drive then cd/dvd drive) and see what it does.

For example at step motherboard+cpu, it should beep an error code complaining about missing ram.

And also change that power supply unit and check for bad capacitors.