lenovo 3000 g400 - laptop not booting / no reaction when power button is pressed

I have a 1.5 year old lenovo 3000 g400 (so no warranty). The otherday when i tried to start my laptop, it wouldn t start - there is no reaction from the laptop (no beeps n led s). Everytime i put in the power cable, the battery LED would blink and get stable after some time but there is no other LED blinking or turning on. In one of the forums i found that by disconnecting all the power cord and battery, i ll have to hold the power switch for 30 seconds and then connect only the power cord directly and switch on the laptop - if the laptops starts booting, it would mean that there is no problem with the mother board. I did the same and my computer booted but again shut off after showing the logo. In another forum I found that such problems can come when the battery in the motherboard is dead or short circuited. So with these I took it to a service center to get informed that there is some problem with the mother board. As a mother board will cost me dearly, i don t think that is possible. Can anybody tell what the reason might be and how i can go about to fix it.

If the prob lies in the battery, I should be able to get my laptop working if I connect it directly to AC without any batteries attached to it. I am suspecting a problem in the power supply chips. Can anybody tell me how to go around checking the power supply chips ?

i checked both the batteries n power supply in another lenovo 3000 g400 n seemed to work well. I also happen to notice that as soon as i try to switch it on, the fan which usually runs at top speeds during the start up doesn t start at all. So i opened up the case and tested the power supply inside a bit. There seemed to be power in most of the portions. But i couldn t check the fan. Can you tell me how to check the fan ? or from where the power supply to fan would come from ?

And yes thanks ghn for looking up this issue