Conflicts: When you install a new software or introduce a new hardware, a conflict may crop up. The new installation might cause an interruption in the normal flow of the system. Faulty and outdated device drivers may also cause the conflict.

Viruses: If your anti-virus software is outdated, several dreaded viruses may be launched, infecting your computer. Viruses can travel through email attachments, execution of .exe files, games, music and the free Internet websites.

Spyware: Another disastrous parasitic software that can cause irrevocable damages to your system and that are not detected by anti-virus software. They can steal your personal information, access your files without your knowledge, pass on your data to a third party without your permission and intrude your privacy by monitoring your online activities. 

Windows registry problems: inconsistencies in the system registry can cause the PC to go volatile. When the system fails to execute well, it comes crashing.