The problem of a computer failing to boot up occurs due to hardware or software problems such as faulty power cables, loose connections, compatibility issues or harmful programs. The exact process of solving such problems depends on the behavior of the computer when turned on.
If the computer does not turn on completely, check if the power cables are loose. Unplug the computer from the power outlet, and plug in a different electrical device such as a radio, charger or fan. If the device doesn't work, the electrical outlet is the problem.
If the computer starts and displays a blue screen or freezes, restart the computer, press the F8 key, and then select Safe Mode. When the computer turns on in safe mode, uninstall any recently installed drivers, scan for malware, or perform a system restore to fix the problem.
In Windows XP, insert the Windows XP disk into the computer, restart the computer, and press any key to boot from the CD-ROM. Press Enter when the Welcome To Setup page appears. Press the F8 key on the Windows XP Licensing Agreement page, and then press the R key on the new page to allow Windows XP to diagnose and fix the startup problem. This process does not delete existing files or programs in the computer.