Welcome to Windows. It does that for more reasons than you can imagine. In order for anyone to be able to help, you will need to provide more information (what version of Windows are you running? What codes or error messages appear? Does it always happen while you are using a certain application or performing a certain action? How long ago did the problem start? Did anything relating to Windows or software change around the same time--new program loaded, new hardware installed, Windows updated, etc.)? What steps, if any, have you tried so far to diagnose or fix it and what were the results?