Vipul:
First u need to check the memory[RAM]. Make sure the contacts are clean. Try moving it from one slot to another. If reseating will not help, find a known good memory stick and test the PC again. Try starting the PC without the hard drive. Sometimes a failed hard drive can halt entire system.
Even if that doesn't work then Check all connections. Remove all devices and leave only three main parts: motherboard, processor and memory. Test the PC with an other monitor. If you still experience the same problem most likely your PC have a failed motherboard or SMPS