cannot click and drag to high light text

I'm presuming you have a Magic Mouse (wireless)

• If you have a USB mouse plug it in
• In System Preferences click on Bluetooth
• Move the cursor to Magic Mouse and delete it by clicking on the (X)
• Using the USB mouse, in System Preferences click on Mouse and then Set Up Bluetooth Mouse
• Once the Magic Mouse has paired with your Mac see if if you can select text
• If you still can't select text try restarting your Mac in Safe Mode to see if you can highlight text and if you can highlight restart as normal and check again

• Left Click and hold to highlight the first word in the line
• While still holding move the cursor down to highlight the lines below