The CPU restarts but the monitor show no sigl

Hello,


my system suddenly shutdowns itself and restarts its self

some times it restarts properly

but some times, though the CPU restarts but the monitor shows no signal.....

after some time keeping it alone undisturbed, later it starts again normally with out problem

can anyone tell me whats the problem


i m using windows xp sp2, intel pentium dual core.. ( HCL COMPANY ) Brought in aug 2008.

In February 2011 i have changed the mother board to " ECS G31T-M7 "