Hey so its my first time building a computer and I am having some trouble. I have already done some research, and looked at the forums here and I can't find the answer. Everything is connected, but the BIOS won't come up.
 
Motherboard: Asus pn5-e sli
Video card: Nvidia 6600GT 512 MB PCIE
RAM: 2 1gb DDR2
Hardrive: 250g SATA hard drive
Power supply: 550 w
 
The CPU fan spins, and so the power must be getting to the motherboard.Everything seems to be connected. I could be wrong though. I am really at a loss for what the problem is. Any help would be much appreciated. Also if I left info, sorry.

Did you connect the AUX 4/8 pin plug to the motherboard?
 
Did you properly install the motherboard is the case? ie. No standoffs under the board were there are not screws.
 
Did you test the PSU? Just because the fans spin does not mean the PSU is good.
 

Sorry I didn't reply. Its just that I was trying to gather some info, and I couldn't respond. The motherboard is properly installed. As for the PSU, the LED that is supposed to glow green isn't glowing. It think that is merely because we didn't bother connecting it. As for the AUX 4/8 pin plug. I must make a confession and this is why it took me so long to respond. I think I know which plug you are talking about but I am not sure. I know that probably makes me seem stupid, but I am really inexperienced so thats really my only excuse. I think I what plug that is, and in fact have been thinking that it needed to be plugged in but wasn't sure because I could find it mentioned in the manual. Next to it is says ATX v 12. That wouldn't happen to be it would it?

It should be a plug on motherboard itself that looks like it takes a male plug with 4 or 8 square holes.
 

Yeah thats how it looks. It has two square holes and then two square holes with rounded edges. Thats it then? Just connect the powersupply male plug with the female plug thats on the mb? You said it looks like a male, and it does, but its actually a female correct? Just checking to see we are talking about the same thing.

Sounds like we are.. the PSU plug should be male and the plug on the motherboard female. It might be the other way around, but we are in fact talking about the same plug.

Yup, it needs to be plugged in.

Thanks everyone!

Alright it works! Well the power LED is working at least. Thanks everyone. The problem is that now it seems to be in sleep mode. It doesn't boot. Yesterday, before I tried this, it would start up, and power light on the front would come on. Now I hit the button and it just glows red, as if it were in sleep or turning off. Sorry to come up with so much trouble.  
 
Thanks again shadowduck. You too roadrunner.

Nice work guys. If you are using XP sleep doesn't work properly. I believe sleep works properly under Vista.

It turns out the problem was much simpler than that, but thanks for the help anyway.