Computer not booting help

First off apologies if this is in the wrong forum but i wasnt sure which section to post this in.
Basically when I try to turn my computer on the power light comes on but the computer fails to boot and doesnt even display anything on my monitor, and then it continues to stay in that state until i turn off the power supply.
At first I thought it was my power supply as my old psu made a terrible grinding sound and my computer was running slowly before it ended up failing to work so i replaced it yesterday but the same problem still exists. I also read that the other 2 things it could be were the graphics card and the RAM which i bought about 6 months ago so I doubt it would be the RAM. I have checked the RAM slots by trying to boot the computer with no RAM in the slots and the computer lets off a beeping sound which I assume is a good sign that the RAM slots are working. I also tried to put in an older graphics card in instead of my current graphics card and the computer let off the same beeping sound, but I am unsure why as the graphics card was securely in the slot but it was also a very old card so I think that may be the problem. I am unsure of what to do so any help or suggestions are welcome.
Thanks in advance.

Hi Paul.
I've updated my specs but unfortunately I dont know my mobo model but its just the stock mobo that comes with the Packard Bell X9610.

Did you have onboard graphics, if yes, remove the graphics card & boot up.

No, I didnt have onboard graphics.

It's a Samsung LCD TV im using as a monitor and I'm using a vga cable to connect it, unfortunately I cant test it with a different cable just now but I don't believe that would be the problem anyway. I'll test it tomorrow and post results on this. Thanks.

The strange thing is I actually had a monitor that worked up until I installed W7 and then once i tried to use it with W7 it would cut out and give an error message right before the desktop would appear upon booting. Dont know if that could help narrow the problem down at all though?

Ok, I tested the computer on another monitor but the same problem still exists.