Unplug the pc from the power. then locate the cmos battery and remove it. then use a screw driver to short the battery connectors in the motherboard fo 5 seconds...

make sure that the memory modules are properly inserted in the slot. sometimes it help by pressing it down a little harder.

let me know if successfull..

Try to power drain the system by pressing and holding the power button while the pc is unplugged from the power outlet,if its a laptop,removed the battery first