I am using intel 915 GAV Chipset.
i was initially having 2 512 Ram Slots installed.
Just today i got another 1 GB DDR Ram and inserted it.
But after that my PC is not getting booted.
I am confused whether the New RAM is not working or is it do to do something with the Blue and Black Colour Slots.
Make sure that the new RAM is compatible with the motherboard (single sided vs double sided RAM can sometimes pose problems). Newer RAM modules have different bank size specifications and may prove incompatible with some older boards. For you to know this, you must read the manual or consult the manufacturer's website / support.
Also try again with different memory configurations like placing only one memory module or maybe mixing them in different slots etc.
The blue and black slots have impact on the speed of data transfer but can not cause the motherboard not to start whichever combination of RAM you choose.