OK here we go.
If your power supply has that on switch turn it on now after everything has been hooked up then press the power button on the front of your computer and watch it come alive.
At this point there's a miniature computer inside your motherboard that's called the bios and it starts up first.
The bios at this time will do a system check on the motherboard to make sure everything is operating properly and then it will check for any and all hardware that may be connected to it.
It then sends a message to each one in turn waking it up and asking it to introduce itself.
This is the time everyone complains about.
But without this check you could burn out your brand new assembly before it even starts.
Each piece of hardware you installed then does a self check and sends back a reply saying I'm good to go.
If the self check doesn't pass then no message will be sent back and depending on the priority of the hardware the bios will either ignore it and go on to the next on or it will halt the computer and put an error message on the screen.
Keyboards, mice and floppy drives have a high priority and failure can cause the bios to stop the machine unless it's turned off in the bios settings.
Hard drives have either a very low or no priority at all.
They can fail, be disconnected and the bios will still go merrily on it's way as if nothing bad has happened.
Usually an operating system has to be installed before you will get a boot or hard drive failure message.
As the screens start showing up you first will usually see what's called a splash screen where the motherboard's manufacturer's logo and other information is usually shown this is where the bios is doing most of the work I mentioned earlier.
After the splash screen you will see a memory check and a screen that will say something like press f2 or press del to enter setup.
If you can catch it fast enough press which button it says to go into setup.
When in set up you are only going to do two things at this time.
When in the setup screen look for a set of f button commands which are usually at the bottom of the screen and find the one that says load default settings. This is usually F5 whichever F button is says to press, press it then wait a few seconds then look for the one that says save settings and exit.
This is usually F10. Whatever button yours says press it then wait for it to save and reboot.
Bios is not made by Microsoft so you wont see a message that says "Are you sure you want to do this?"
You're expected to know what your doing if your in this section and so usually will not see anything except maybe a quick flicker in the screen that lets you know if it's been done.
So just press the load defaults button wait a few seconds then press the save and exit button and wait for the computer to reboot.
If everything goes properly then you will see the same screens again and this time do nothing at the bios screens just check inside the case to make sure all fans are running and wait till the bios finishes doing it's job.
The finish here is somewhat anticlimactic after all the work you just went through.
If there's anything at all displayed on the screen it will be the last thing that the bios did and had no clean-screen command after it to clear the screen.
BUT if you heard no beeps or maybe just a single beep and see no error messages on the screen then you did good and your ready to insert the operating disk into the cd/dvd drive and install your operating system.
So at this time press the button on the disk drive and insert the operating system disk, close the drive by pressing the button again then press the power button on the front of your computer to turn off the power wait about ten seconds then press the power button again to turn it on.
Follow the instructions on the screen as the operating system goes through its setup and your finished. Sort of.
Its a good idea at this time to connect to the internet and go through all the updates your system needs at this time.
If your running any windows later than XP or the latest UBUNTU Linux distribution all you need to do is hook up your dsl to the lan connection on the back of the motherboard as shown here
and go to the update feature of your operating system and let it run its course loading and installing all the needed updates to complete your system.
If your on dial up I suggest you go to a friends house that has dsl and use theirs to update the operating system.
Dial up would take so long that I don't even want to think about it.
Another solution is ordering/buying an update disk from the manufacture of your operating system.
Microsoft has these and Ubuntu does as well.
I don't know how much Microsoft charges to ship an update disk but the last time I looked Ubuntu Linux was about ten dollars including the shipping charges.
Reputable Linux distributors only charge for the disk and shipping and handling as the Ubuntu operating system is free to alll who want to download from their site at Ubuntu.com
So depending on the type of Ubuntu Linux disks you order anywhere from ten to fifteen dollars should cover everything.
OK your up and running with the new computer assembled by your own hands.
After the initial check then os setup and upgrades you should power the computer down then unplug it and press the start button on the front this will drain any current left in the circuits.
This is the time I now finish installing any second hard drives or DVD/CD drives or memory readers I have to put in.
Nope I did not forget or overlook the disks that came with the motherboard or graphics cards you may have bought.
Today's operating systems such as Vista, Windows 7 or Ubuntu 9 series will have all the drivers you need to get your system up and running.
After the OS is installed and updates finished go to the manufacturers web site and download the most recent drivers for your particular hardware.
I have in fact on one rare occasion uninstalled the motherboard drivers that I downloaded from their site because everything ran better with the drivers that Windows installed.
If you have bought a high performance graphics card to improve your system's performance then downloading the manufacturers drivers is a must to get the best that your card can deliver.
Now is the time to hook up the fan on the side panel you have had off all this time to install the parts to your system and put the panel back in place.
Remember when tightening the screws to it just make them snug.
Computers are not car engines or cabinets or anything that gets a ot of rough moving and slamming around (if you want your system to last long that is)
This also helps to prevent any skewing that can come from over tightening screws.
You have just finished your computer!