I put together a pc but it wont power up. The motherboard I bought came with a picture of the motherboard and all its parts, but I noticed that the motherboard is missing a piece that is on the picture. The missing piece is located my the four pin power connecter. This is probably a stupid question but is this motherboard screwed?

First off, you really should give more information. What is your motherboard? You said a piece is missing, are you talking about a pin, a connector, what? Without this info it's a little hard to try to help. Always try to give as much info as possible. You will get better results.

the motherboard is a BIOSTAR 423 Socket model M7TDR. Im not sure what the missing piece is.Its a black square with only two pieces connecting to the motherboard.

I think what you are talking about is a heatsink for the motherboard North bridge chipset. That won't keep it from powering up. I would check and see if the LED power LED on the motherboard is lighting up and staying lit when you switch the power on. If it is then I would suspect the motherboard to be faulty, or the Processor. If the power LED does not stay on when you turn the PC on, then I would suspect a bad power supply. Hope this helps.

if the boards power lite is on, then you may have wired the front panel connectors incorrectly, meaning the power on button isnt doing anything when you press it. Also check your RAM is seated correctly. Also check the obvious, for example is your power lead good?

Manufacturers do not always update their documentation when they make minor changes.

check that the voltages are correct at all the pins at the power supply connector. do not disconnect from mother board during testing. make sure you are getting a power good signal. pin 8 (gray)(2.4 - 6V ok 5V nominal) wilke is right. the documentation rarely exactly matches the hardware.