There is no magic button to press - the closest is to rebuild the Operating System but you will need the OS Media and will also lose any added software you have put on and will need to save important files of your own on removeable media if you wish to preserve them.
Alternatively you can attempt to discover the remedy of the specific problem that makes you want to restore the machine to its original state.
It is very easy to have the machine return to a "restore point" at a time in the past when it was working OK.
You may do well to place another question indicating the actual problem you have - people on here may have an easy solution for you.
Good luck...
Peccavi, June 2010
