My computer powers up but does not boot

Can you load the BIOS? 
 
This is usually done by holding down the <del> key while powering on.
 
If you can the next thing I would check is the boot drive, specifically can the BIOS see your normal C: drive.
 
If you can load the BIOS and the C: drive is visible, I would try booting from another device i.e. the CD Drive.
 
Difficult to say what to do next...

Yes start with the bios. 
If you are still stuck this forum here is the best nerd squad for issues. They have never failed me in 20 years. 
http://forums.ncix.com/
 
We also have a computer forum here but most of those guys also check this hardware forum to as it's almost the same idea. 
 
   Bitflipers comment about beeps is also a big clue, Modern Mobos like mine also have a small LED with numbers and this gives you a trouble code,, You'll need the Mobo manual. 

Another option:  The video device you're connecting to the monitor for whatever reason is no longer the default device.  This can happen with systems that have on board video + a discreet graphics card.
 
If you have a motherboard with video output, try connecting your monitor to that during power up and see if you get anything.  Try any and all other video outputs, including and in particular good old analog VGA.

If you are Linux savvy, you can boot to a USB drive to diagnose.

johnnyhenderson
Hey all,
 
I am having an issue, whenever I start my computer it powers up, led lights on the case are on and the fan is working however nothing happens, the OS does not boot, the screen does not go on. ( yes my screen works 100 % , already tested it). So when i turn the comp back off, the led light around power button turns off however the led light at the upper case still stays on and the fan even spins harder, can anyone please help me out ? removed some cables inside and ram but with no result..
  
I didn't find the right solution from the internet.
References:
 

Is this legit or are the references we can't read spam of sorts?
A couple of thoughts. I assume you are talking about case fans or fan. Although it's weird for a case fan to spin faster upon power off, if the OS isn't booting. How do you know the OS isn't booting?
One clue is if you have a video card with fans - then upon power up of the case the video card fans usually spin faster until the OS kicks in and the graphics software stabilizes the fan speed, so that they noticeably slow or quieten down.
 
It's always hit and miss. If I were a betting man, and you hadn't moved or knocked the PC recently, I would say change the CMOS battery on the motherboard and reboot. The CMOS battery is the small flat disc battery on the motherboard. You can pick them up at most convenience stores. Just get the same type - the number is on the top.
2 cents

Yup, power supply should be the first thing you should check. Get a spare power supply and test with that.  Just unplug the existing power connectors, and hook up the leads from the spare.  No need to install it physically.
 
Unplug all of your drives, internal and external, until you can get a good POST.  Unplug everything else external except for the keyboard and monitor.
 
If you have any add-in cards (PCI or PCIe) temporarily pull them out.  If you don't have integrated graphics, you might have to get a spare GPU to test with.
 
Test your RAM one stick at a time.
 
If you do all this, and still don't get a POST, the motherboard is probably dead.  Check your CPU socket and make sure everything is still seated.  Maybe pull the CPU and reseat it with new thermal paste.
 
No need to worry about the hard drive or OS until you get this far ...