AutoSleep problem? Mabey?

Ok i am having a problem with a computer obviously. I get power to my computer, yet my moniter, keyboard and mouse get no signal. At first i thought it was the power supply, so i changed out the power and cables. Not the problem. Then i decided to take it to a professional to ask him what the problem was. He looked at it told me everything was plugged in correctly and all that. He suggested that the problem might be that my motherboard/cpu might be the problem. So i bought a new motherboard and cpu and installed them, also getting new RAM that would work with the cpu/motherboard. Everything is connected right again and all that. Yet im still having the same exact problem... Moniter keyboard and mouse still have no response (moniter goes into its "sleep mode" as if the compiter is off... ) Is there any way to fix this? Or would it just be better to get a new computer (wich i really dont want to do lol )

 

When you boot the machine, does it go through POST? Is there a keyboard error on boot? Did you plug in both power cables to the MB from the power supply? Can you get into BIOS? When it boots, does it go to a black screen with what looks like _ flashing? Also, can you boot to a bootable CD?

 

Power cables are in, no i dont get any screen whatsoever. When i turn my computer on the screen stayes in sleep mode, mouse and keyboard dont work at all either. Also everything turns on but the power light does not turn on? Fans, hardrive and disk drives all have power, but the monitor and keyboard/mouse have no function? like i said i already replaced motherboard and cpu. Replaced power unit. Had a guy at CompUSA put it all together. What else could the problem be?

 

OK, you really didn't answer anything I asked, we established you have new parts, that doesn't mean they are good. My questions which weren't answered were/are;
Did you plug in both power cables to the MB from the power supply? You do know there are, in newer computers, two power cables that must go in the Motherboard...and just because some guy at CompUSA said it looked okay, doesn't mean he didn't miss it. As a side note, if you have a newer video card, it too will require its own power cable.
Can you get into BIOS? - As in, can you hit the "del" or "F2" and get into the BIOS?
Also, can you boot to a bootable CD - did you try this? New question here, does the computer itself go through normal sounds, do you get a normal beep when it boots, or a series of beeps, or nothing? Last but not least, did you try hooking this up to another monitor to see if it works? Your monitor could be bad.

 

Then there's the one major part that hasn't been replaced: Video card.

 

That is why I asked for beep codes - most, if not all, motherboards will beep code when a video card is bad.

 

Right you are...We should probably know what motherboard, vid card, processor we're dealing with here..