If your computer starts up normally, but then has a problem once it has started, such as the screen freezing or it is running very slowly, there are a number of tricks you can try.
1) Restart your computer
This has become a cliché but it solves many desktop and laptop problems. It's quick and easy so is always worth trying first. If your computer screen has frozen you can usually force a shut down by holding down the power button until the computer turns off, then start up again.
If it won't turn off, you can force a complete shut down - with a desktop PC by turning off the power at the mains and a laptop by removing and replacing the battery.
Back up your data to avoid losing it if your computer breaks
Back up your data to discs or an external hard drive to avoid losing it if your computer breaks
2) Back up your files
Even small problems, such as your computer running slowly, could be symptomatic of a bigger issue. To avoid losing important files and photos if the problem escalates, back up all your files – the free Which? guide to keeping your data safe explains how.
3) Run computer security checks
If things aren't working as smoothly as they should or you're frequently experiencing problems, run a security software update. Some particularly malicious malware or viruses can stop your computer from starting, but more commonly they will just make your system sluggish. A security scan will put your mind at rest and will let you rule out malicious attacks at an early stage.
If you don't have security software installed, or are unhappy with your current security, installing Which? Best Buy security software will help keep your computer safe from attack.
4) Remove recently installed programs
If your computer has problems just after you've installed a device or a software program – whether you've installed it from a disc or downloaded it from the internet - uninstall the last piece of software you put on your system. To do this safely and fully, go to the Windows Control Panel (accessed from your Start menu) and select 'Add or remove programs'. Once you've uninstalled the program, check for improvement. If everything's working OK again, you can try reinstalling.
5) Check for duplicate programs
Problems can arise if you have two versions of the same program running (for example, if you've reinstalled a piece of software to get the latest version rather than using the program's update option). You can check if you have multiple versions of the same program running using the Windows Control Panel, which lists all programs you've downloaded to your computer. If you spot duplicates, uninstall both versions, and then try reinstalling (if you're installing from a disc, you may also need to check online for updates).
6) Don't use more than one antivirus program
It's vital to protect your computer with appropriate security software. But running two antivirus programs on your computer – for example, running Microsoft Security Essentials, which comes free with Windows, and then installing an extra antivirus program from a company such as McAfee or Norton – can cause conflicts on your computer. This can make your computer sluggish and at worst can cause computer crashes.
If you have two different antivirus programs installed on your computer, make sure only one of them is active. Find out which security software Which? recommends in our review of online security software.
7) Check for and install Windows updates
This is a straightforward way to ensure you are up to date and should improve the performance and reliability of your computer. You can set your computer up to check for and install Windows updates automatically. If you haven't already been running updates regularly then it may take some time to download all updates, but it's worth it.
8) Carry out a system restore
This is a powerful and effective tool and will fix many PC problems by reverting your computer system to the last state in which it was working well. Go to Start> All Programs> Accessories> System tools> System restore or in Windows 7 just enter 'system restore' (no quotes) in the search box.
Once you are in the main window, if you have an available restore point the date will be highlighted in bold. Click that date and simply follow the step-by-step wizard that will take you through the process and will even restart the computer for you. If it has restored successfully you will get confirmation.
Windows 7 discs
You can use your Windows operating system disc to repair many computer problems
9) Conduct a system repair
You will need your original Windows operating system disc for this. Put your disc in the disc drive and restart your computer. When the computer turns on, you will see an on-screen menu with a number of options. Select the repair option - in Windows XP you do this is by pressing 'R'.
WARNING - DO NOT select the option to install Windows – if you do so and proceed with a full Windows installation, it will wipe your drive and re-install Windows from scratch. This will lose all of your data. Using the repair option will not affect your data, but to be on the safe side, back up your files before trying this method.