computer will power on, but won't boot

I have a custom-configured computer (bought through BestBuy) that is about 3-4 years old. The other day it froze, so I turned it off and then proceeded to try to turn it on again. Now, the computer will turn on, but it won't boot, nothing is displayed on the monitor and no sound comes through the speakers.
I have tried a different monitor that I know works and still nothing is displayed. The CD and floppy drives are being read, but emergency boot disks have no affect. The keyboard and mouse both seem to not be recieving power, as none of the lights on them are lighting up.
Does anyone have any suggestions/ideas/help? Thanks in advance.

(^^;(There's many similar questions.)

Read them for detal. But roughly,

Test all the parts on another PC.

Then, remomove cmos battry, leave it a few days.

Flash bios by autoexec.bat.

Things to try:
New psu
New videocard
Clear cmos/new cmos battery

I assume you aren't getting any beep codes that might help find the problem?

i have replaced CMOS battery and reset the CMOS, both to no avail. I have the speakers turned on every time i try to start the computer and I don't hear any beeps or anything, so I assume that means i'm not getting any "beepcodes".
how do i "flash bios by autoexec.bat"?
Thanks again for the help.

If you make sure that CPU, memory, Video Card and so forth is good.

Then you can flash bios, if the floppy is being read. This is the last resort but worth trying before mobo exchange.

Are you making sure that it's motherboard(bios) failure?

Now, download your bios from your PC's manufacturer.

If they don't have it, you must check the M/B to take a look at bios version, chipset. types of M/B.

And find the replace for your PC.

Take a coffee break!

well, i took it to a computer repair place and they told me that it is a bad motherboard. i was wondering how hard it would be for me to replace the motherboard and processor (i would love to be able to save the money on labor by doing it myself).

If you are comfortable working in your computer, its not very difficult. Lots of "How to's" on the web. Be sure to back up everything beforehand though (put the hard drive in another compouter as a slave), since you may have to reformat afterwards to make everything work.

(^^;( Yeah! If you enter into this, you can't help doing this.)

It is too interesting to stop this for me. Recently even girls are likely to do so.

As a matter of fact, it is far easier than plastic-model making. (No kidding!)