PC turns on, but monitor doesn't show anything?

[SpywareDr]

I hooked it up all properly, but when I start it the CPU fan starts working

All that means is the CPU fan is getting power from the power supply, (through the CPU_FAN connector on the motherboard).

... the LCD monitor doesnt show anything on the screen. It just keeps blinking its orange light(that's when monitor is on but the PC is off).

Monitor is fine, also tried with a different monitor, but no difference.

The blinking orange LED on the monitor means it cannot detect a working computer. (Check the cable and connector[s] ... and the computer of course).

Until the computer is working and sending something to display on the monitor, (through a working, properly attached cable), the monitor will remain blank ... simply because it isn't receiving anything to display.

Also I tried different CPUs(it's believed that both CPU's I used are 99% dead) but still the monitor won't show anything on the screen.

A computer cannot think without a "brain". The CPU is the "brain". If the CPU is flaky/dead, the computer is too stupid to be able to send anything at all to the screen.

There are no beeps signaled when the PC starts up.

A computer cannot think without a "brain".

All I can say is that when you open the case you'll see an orange LED on the motherboard.

All that means is that the motherboard is getting power from the power supply.

What's the problem here?

The first thing I'd do is take a quick look for bad caps, then plug in a known-good CPU, as well as known-good RAM, and then try powering it up again.

If it still fails, try a different motherboard.