last week my friend send me their old motherboard videocard ram and power supply through the mail, they all apear to be in working order however when I turn on my monitor it receives no signal, its as if there isnt any pc connected to it at all.

To figure out which part was failing I ordered a new motherboard with onboard videocard, a dvi cable in case it wouldnt work with my old vga one and got myself 2 vga cables and 1 dvi screen and 1 vga screen. However no matter which combination I use I can't manage to get a signal to the monitor.

I must be missing something simple like a giant red on button on the videocard or something. Does anyone have any suggestions?And the monitor definitely works on a different system?  Have you checked the RAM works?  What motherboard and CPU are you using?  Have you tested the power supply on a working system?the monitor works cause im using it to write this, I got 2 ram sticks from my friend that are supposed to work on the motherboard I got with it and my new motherboard uses ddr3  so I had to get new ram with it so I assume it works as I unboxed it this morning. I cannot test the power supply because the pcs I have that work are all ancient and dont have the proper connectors for it however it does make my fans spin and computer boot up so it works at least somewhat.

CPU amd fx6300 
Motherboard m5A78L-M usb3Since it could be any of the things Cameron mentioned as well as others you should post the complete specs...I'll write down my specs tomorrow when I have access to all of them cause I don't know them by heart but it shouldnt matter too much as I used 2 motherboards with each their own cpu and ram one with an on board video CARD and another with a dedicated videocard. Of course multiple things could be wrong but it WOULD be quite the coincidence to RESULT in the same exact problem right?

Now that im thinking of it I'm starting to believe that it has to be the power supply as it is the only part used in both builds and it's not very new.
Could it be that the power supply still has enough power left to turn on the lights and fans on my parts making me believe it's working properly while it doesn't actually have enough power to make the videocard capable of sending out any signals?Yes...pc 1                                                                       pc2
motherboard:  Gigabite GA-EP45-DS3                  Asus M5A78L-M/usb3
               
cpu:  INTEL Pentium D 805                                      AMD FX6300

ram:  Corsair Dominator 2048MB X2                     Kingston HYPERX Fury 8GB 1866MHZ

videocard:  Sapphire HD4870                                Integrated ATI Radeon™ HD 3000

parts used on both machines:

power supply:Be quiet p6-530w pro

hard discs I tried:
western digital WD3200AAKS
Seagate Barracuda 7200.10 RoHS
and a 3th one which name I can't see as its used on this pc which is a tiny abomination and a totall pain in the *censored* to take apartPSU...that's my guess.

Doesn't exactly have glowing reviews...