I'm at a total lost here. I'm building a computer for the first time and it's not booting up at all. What it does:

I switch on the PSU and the motherboard is powered on (the green light is on) but when I switch on the computer the fans only turn on for only a second and then turns off. No signs of the boot screen or anything on screen. I made sure the PSU connectors are in place but no luck. Is there something I'm missing or does it sound like something is faulty?

Computer Specs:

Windows XP Pro
Asus P5N-D Motherboard
Intel Core 2 Quad 6600
G.Skill 2x2GB DDR2 800 RAM
Corsair TX750W PSU
nVidia GeForce 9800 GTX+

Hard Drives:

Western Digital Caviar Enhanced IDE Hard Drive 120GB
MDL: WD1200BB - 00GUA0

Maxtor DiamondMax 10 PATA133 HDD 200GB
MDL: 6L200R0

I've had the hard drives for a while but they still work on my other computer.There should be a 24-pin ATX power connector and a four-pin auxiliary connector plugged into your motherboard, but more likely I think it could be something with the front panel connectors, which are a little trickier. Make sure to read your motherboard's documentation, as it seems like sometimes the connectors go in "upside-down", and it's really hard to tell which way it plugs in just by looking.

Also, do you have speakers plugged in? I think you need to have them in to hear the motherboard alarm (I don't think motherboards have built-in alarm speakers), but if you hear a beeping sound it usually means something basic is going on, like a wire isn't hooked in correctly. I remember the first time I built a computer and I actually forgot to plug in the supplementary power connector into my graphics card and panicked for a second—and nowadays, some cards even need two of these plugged in.Are all motherboard standoffs in place?

Did you apply thermal paste to the CPU?OH yeah, make sure the standoffs are in place and the motherboard isn't making contact with the case in any way that could short it. Also, if you DROPPED a screw or little metal doodle in there anywhere it could be making contact with the motherboard tray in some weird way… I've taken everything out of my case, held it over my head and shook out a little case screw before, but it wasn't what was causing the issue. The best thing is to go through your motherboard manual again and follow the instructions carefully and double check everything is plugged in correctly, though; CLEANING out the case or trying to boot it up outside the case should be like one of your last resorts.

http://fixingmycomputer.com/

Here are some flowcharts; the top one looks like what you need. 750W should be plenty enough for your rig, especially since you don't have a power hungry multi-GPU system.I applied thermal paste to the cpu and the connectors are in place, double checked to make sure they're secure.

What to you guys mean by motherboard standoffs?

I will take a visit to that site you posted Hearts on Fire.The standoffs are the copper-colored screws that look like this: http://www.evercase.co.uk/images/Accessories/MotherboardStanOff2.jpg

You screw them into your motherboard tray before placing the motherboard down and they separate the motherboard from the case so it doesn't ground/short anything of the electronics. They also secure the motherboard in place on the tray.Ah okay I do have some of those. I will try to put them in now. I hope I didn't do any permanent damage. I will tell you how things go, thank you so much for your knowledge!Yep that's was it, the standoffs. It's running now and it works like a charm. I want to thank you guys for helping me out! I truly appreciate it!COOL
Glad you got it going.