Sometimes you just need to take a break, get up from the computer and stretch, walk away. Do another activity to get your mind going, thoughts will soon start to filter in and you will have another idea. My most riveting ideas come while I am in the shower ! And sometimes while I am driving -- I have to pull over and write it down quick!
Make sure you keep journals with you. I have one in my car, by my bed, at my desk, and a small notepad in my purse.