PC not turning on !! pls help !

HI ,
I was looking into my friend`s computer.Its a XP , P4 pc. Now i just wanted to see the brand name of the RAM. thus i unjacked the ram , saw it and hooked it on .... now since that the PC is not turning on .... neither there is any light coming on the motherboard ( the small green lights that glow after pc is started ) ??

Any idea what this can be ?? all helps are appreciated....

Thanks

I think u have to once unplug all the wires and plug them once....Once the system do like this