Assuming it isn't just a case of a rogue orange sitting on the ctrl key, or it isn't jammed on by another means as popatim suggested, the 'sticky keys' setting might be the issue.
If you're running Windows 7 then go to Control Panel > Ease of Access Centre > Make the Keyboard Easier to Use. If the 'Turn on Sticky Keys' box is checked then uncheck it.
If you're running Windows XP then access this by going Control Panel > Accessibility Options and then unchecking the 'Sticky Keys' box.