I can't open any icons on the desktop or some things in the start menu such as the control panel, when I try to the screen goes blank for a few seconds and then recovers. Also when I try to download anything it says I do not have administrative powers but I can't open up the control panel to change this.:(

You obviously don’t have administrative rights and therefore you are logged in as a Restricted User.

You need to login as an administrator and change the setting of your username (that you logged in as previously) to a Standard User (this is done in the Control Panel under User Accounts) where you will be able to change system settings and install programs/download files.

If you are on a Domain, you will need to enable this from the server (e.g. if you are using Active Directory) and login to your PC as an administrator on your local computer (not the Domain) and then ADD your username to your PC (this is done in the Control Panel under User Accounts).

Hope this helps..