This depends on how your computer was setup. Most home computers have the administrator account disabled. First, search for Computer management, it may be found by right clicking on the start button or typing in the Run Command. Then look for Local Users and Groups. Open Users and see if the Adminstrator account is marked disabled, if it is marked disabled then try enabling the account. If you do not know the Administrator password, it may be possible to change it but generally requires administrator rights.
This step assumes you know the Administrator password. Sign out and then sign in as administrator. Go to Local Users and Groups and open the Groups section. Double click on Administrator Group and a pop up window will appear. Chose add and enter your USER name, click on Check Name; if this works correctly, you will see your user name underlined. If your name does not seem to be recognized, change the location to local computer.