my photo library will not highlight? why?

Care to elaborate? With the amount of information you've provided it's impossible to offer a solution. We can't see your computer so we need to know the details of your problem and setup, i.e.:

• what system are you running?
• what version of iPhoto are you running? Or are you running the new Photos app?
• upgrading from what to what?
• where is your library located?
• did you apply any updates or upgrades just prior to the problem occurring?
• are you running a "managed" or "referenced" library?

• what type of Mac?
• how much free space on your boot drive?