One of the main reasons why a computer may keep shutting down is overheating. If the computer is overheating, it will automatically shut down in order to protect those vital parts that may otherwise be damaged by the heat.

     So shutting down is a good thing. It helps protect your computer and your files. It's a safety measure not a fault!

     Even the most non-technical computer user knows that a computer makes a noise from time to time. That noise is a fan designed to keep everything cool, and it works much as a thermostat may do on your central heating system. When the heat in your machine reaches a certain temperature the fan (or fans) will kick in to fan cooler air over the components, and as the heat reduces to the correct level the fan will switch itself off again.

      If your fan seems to be coming on a lot, and staying on longer, it's a sign that you need to check things over.

The most obvious place to start is the vent holes or grids. All machines have them, and they're designed so that the fans can suck in cooler air from outside the case. Desktops are particularly susceptible to getting these holes blocked with dust. The unit is placed on the floor under a desk and forgotten about. It's time to bend your back and check the vent holes.

     I've seen people take a duster and wipe a lot of dust off these slots, but if you do that, all you're really doing is pushing the dust to the inside of the case. Far better than to take a hoover to it and vacuum all the dust up.

     Whilst you've got the hoover in your hand, take the side off your case and take a look at the fan (or fans) and you'll probably find that these are covered in dust too, and that makes them far less efficient.

      WITHOUT TOUCHING ANYTHING WITH THE HOOVER, give the whole lot a good hoover up and make sure all the dust is sucked up off your fan and from all the corners of your case.

      Nine times out of ten these housekeeping measures will have your computer up and working OK in no time at all. It's very rare for a computer to keep shutting itself down due to software or hardware failure, and an accumulation of dust induced overheating is far more likely to be the problem.

Curing this problem first is both cheap (as in free), effective, and usually all that's required.

There's no easy way to determine exactly why a PC won't boot (we're assuming that you tried booting from an optical drive or a bootable USB disk, and it failed), but the following steps will take you through the most common hardware reasons for a PC that won't load Windows.

1. Check all of the external cables, including the power cable. Confirm that your monitor is turned on.

2. Do you hear beeps while the PC tries to boot? Write down the number or the sequence of beeps (for instance, one long, three short) and search the Web to learn their meaning. If you know the manufacturer of your BIOS, that will simplify the search. For example, try a search for "Phoenix 1-2-2-3 beep code" (for a PhoenixBIOS PC with a pattern of one beep, two beeps, two beeps, three beeps); in this case, you'll see that the PC has likely experienced a motherboard hardware failure. Even if you don't know the BIOS maker, you should be able to determine the issue this way.

3. If your PC doesn't produce beeps, open the case and verify that the internal cables--especially cables from the power supply and cables linking the hard drive to the motherboard--are properly connected.

4. Make sure the RAM is properly seated; remove and reinsert it, and try booting with one RAM stick at a time (if dual RAM sticks are not required, of course). If you have a spare RAM module or two, try subbing them in.

5. Your system's power supply may have gone bad--many are cheap and prone to failure. Try connecting a spare power supply to your system (you needn't install it inside the case), and see if the PC will boot. Don't be tricked by whirring fans: A power supply may have enough juice to keep the fans going, but not enough to power everything else.

6. If your PC has a discrete graphics card, try removing it and attaching the monitor to the integrated graphics connector.

Finally, if all of the above steps fail, you're probably dealing with a bad motherboard or (less likely) a fried CPU.

     The minute your computer's hard disk starts to act flaky, make sure you have an up-to-date backup. Then you can do some simple diagnostics and repairs. Both Windows and Mac OS come with built-in hard-disk utility software that scans your hard disk for errors and attempts to fix them.

1. Double-click on My Computer icon to open the My Computer window.



2. Right click the disk that you want to diagnose and repair.





3. Choose Properties from the File menu. You should see the Properties window for the drive that you selected.

4. Choose the Tools tab.




5. Click the Check Now button under Error Checking Status.




6. Checked  the two options "Automatically fix File System errors" or "Scan for and Attempt Recovery of Bad Sectors"



7. Click on Start.