Monitor Shutdown

When i start up my PC, everything seems ok. It goes through all the motions (press F1 to continue etc.) Then just after the windows logo appears the monitor shuts down & the red light at the front of my PC is static. Sometimes it gets to the main screen & then shuts off. i have no trouble when going into set-up, it is when windows starts proper. Was told my Graphics card was U/S, bought a new one, no difference, on the few occasions it has gone to the main screen, no “found new hardware” comes up. Any help please !!