|Well, as you haven't given us any details about your pc, no one can help.|
You might find there is a recovery partition on your pc, in which case, you need to go to the manufacturers website, to find out how to get the recovery to work.
You will need to press a key on boot up.
Now, if you don't have a recovery partition, then you will need to get recovery disks, so I assume you didn't create them when you bought the pc,
You will need to go to manufacturers website & buy some.
A thank you would be nice, if I have helped.