There is no button to press to do this...
To achieve it you need to reload the Operating System from scratch... You will lose any applications, files and device drivers added since new. You will need the OS media.
To overcome the problem(s) you have (you do not say) you might try returning the machine to a "restore point" of a date before the trouble started.
Sometimes it's best to fix the problem.
Another question with a description of the specific issues you have with it may help. A "fix" might be quick & easy.
Good luck...
Peccavi, September 2010
