Computer Turns On, but NO Display on Monitor

Hi guys,

I just started my PC after a while & it turns ON, lights turn on, but there is NO Display on Monitor.

I did some research on Google about this issue & did a few things.

1). I removed all the hardware, except processor & power supply. Turned On, but same issue.
2). I tried after removing ram, & then by switching ram slot, but still no use.
3). I removed my HD 3450 512MB graphics card & plugged monitor in Built-In Monitor port & Vica versa (In Graphics Card), but no use.
4). I removed hard disk & DVD rom & changed their power cords, but no use.
5). I removed the computer cord, & pressed & hold the "ON" button for 30 to 60 seconds, but no use.

It was working fine a couple of weeks ago, but then I turned on & it was not working anymore. By the way, when I turned on it acted a little weird before going dark. Actually when I turned on, it took a long time to get to display & then window was also working weird, then I restarted a couple of time & I though it was my hard disk, (who sometimes have power cord issue that works fine if we change it, but its not that).

Any idea how to fix this issue or what is wrong with my computer?

Thanks.