Monitor / PC problem

Hello, Just wondering if any of you can help with the problems i am having with my main pc and monitor. The monitors' power light is flashing but not coming on. According to the samsung website it says it is on power save but i cant get it to turn on. The PC is running as i can hear the windows noise etc With the PC when i try it my old crappy monitor it shows it logging on with the windows sign but then it just goes to black screen though the pc is running (I can move the mouse and hear some of the windows sounds). one time i tried my main pc on the newer monitor (got nothing) so unplugged it and plugged in the old monitor and it was working but i tried to switch users to my main account and then the picture went. I have plugged in my older pc to the newer monitor and that doesnt work on it either but the old pc does work on the old monitor. I am completely lost. I dont know if this is hardware or software. Sorry if this is a bit muddled.

Hello mattem, Before we can figure out what's malfunctioning, can you give me the make and model of each PC an monitor you are using? And could you let me know what combinations of cables you are using? (IE, are you using a DVI-I cable for the new monitor and a VGA cable for the old monitor?) Have you also recently modified the contents of your main PC in anyway? In particular the graphics card? Cheers, Nahumi