Computer Stucks when Booting

There might be one of several problems, go through the list below. Remember to follow then in sequence. (I do not guarantee the solution or warrant for any damage caused to your machine or you during these processes).

1- Try rebooting again and this time let the scan-disk run.
2- Let any boot time Antivirus scan to complete.
3- Check if you have installed any new hardware or software. if yes then follow these steps:
a) Uninstall/Unplug that software/ hardware.
b) surely you might say how you will perform an uninstall, here it is try booting through safe mode, for that:
i) restart your PC and as soon as diagnostics complete, Press F8
  ii) select Boot Operating System in Safe Mode.
    iii) Uninstall the software.
Does any of that worked, if yes then fine, if not then check for these:
1) Plug out your RAMs clean the terminals using CTC (Carbon Tetra Chloride)
2) Switch on the system while keeping the Casing opened, check what do you feel about the processor fan speed.
If it seems to be slow. Replace it. (During my 18 years career I found this the most occurring problem. (but do not try it first)
3) If fan speed is fast enough to keep the processor cool upto desired Temperature then, Plug out Processor and Heat Absorber (also heat sinker  and heat sink). Apply almost 3-5 grams of Coolant Paste at point where processor and heat sink meet.

If you are still having problem.
I'll prefer you to go to a professional for more checkup. You might have to replace one or more parts of your PC to be replaced.

Hope that will help most of the people out there.
Take Care
Allah Hafiz.