External Power Issues
Check the main power source for your computer. Wall outlets can die or be switched off, and plugs can come out of the wall outlet. If your machine is plugged into a surge protector--and it should be--make sure the surge strip is plugged into a working outlet and the indicator lights are illuminated. If the surge protector has taken a “hit,” it may be destroyed or may simply be offline. Unplug your computer and monitor from the strip and press the reset button. If the indicator lights return to normal, plug your computer back in. If they do not light up, replace the surge protector. Also, check that the power plug is firmly seated in the back of your computer. If the power supply on your computer has an on/off switch, make sure the switch is on. Do not change the red voltage indicator. Check the AC Adapter brick on a laptop to make sure the indicator light is on. Try using an identical AC Adapter or a universal AC Adapter.
Internal Power Issues
Power supply boxes on desktop models deliver five different levels of power to devices on your computer. Just one of these levels can go out and the computer may otherwise look like it is turning on normally, but the hard drive will not be able to boot. If possible, test your power supply. Testers are relatively inexpensive. Replace the power supply with the correct type and wattage of power output for your machine. AC Adapter port failures on laptops are common. If the silver post inside your AC plug-in point is wiggling in the socket, see a professional.
Motherboard Issues
Look inside your desktop case. A green or amber light should be illuminated on your motherboard when the machine is plugged in. If no light is on, it is likely your motherboard has died. Unplug the computer and remove the silver, nickel-sized clock battery from the machine. Press the power button to discharge the motherboard. Replace the clock battery and the power plug, and attempt to boot the machine. You can also try resetting the motherboard jumpers, if you know where the tiny jumper posts are located. This kind of motherboard resetting is not possible on most laptops.
Other Problems
A bad device, such as a bad RAM stick, video card or other PCI card, can cause boot failure. Remove all PCI cards from the desktop and all PCIMIA cards from a laptop. Remove one RAM stick and try to boot. Test other RAM sticks alone, as well. If the computer boots on one stick, but not when another, or two sticks are present, replace the bad stick. If both RAM sticks boot, start adding PCI/PCIMIA cards back in, one at a time, until a card makes the boot fail. Replace this card.
Hard Drive Breakdowns
It is possible, for several reasons, for a hard drive to fail catastrophically. Replace the drive with a spare drive and try to reinstall Windows on this test drive. Or, try to access the drive by removing it and placing it in an external USB drive case or "slaving" it to another desktop. If the machine boots to the install disk, or the drive shows up on the other machine, your main hard drive may be mechanically broken as well as electrically damaged.
Windows Problems
If your computer tries to boot to Windows, but then shuts down or “blue screens,” try booting in Safe Mode by pressing F8 when it is starting. Choose "Safe Mode" or "Last Known Good Configuration." If this fails, insert your Windows setup disk in the CD tray and reboot to this CD. When prompted, choose “Recovery” options and then type “Chkdsk,” or “Fixboot” into the DOS screen. Your Windows installation may be repaired in this manner. Otherwise, you may need to do a full reinstall of Windows to recover boot capabilities.