Petter,
I know it’s pretty late in the day to respond to your inquiry and by now I’m sure you’re up and running again. Even so maybe this’ll help you or someone else in the future. I’ve just begun using Sketchup, version 2014, and similar to you I’ve already had the same issue. Suddenly one day my measurements toolbar wouldn’t accept a keyboard input. Seemed to be locked and frozen. Searches in the knowledge base and‘net returned schooling on how-to-use-this-feature kind of replies. Useless. Might have made sense to other readers not experiencing the issue but to me, and I suspect with you, however, the well-meaning helpers missed the point. This problem seems to be very uncommon as evidenced by the dearth of information on it anywhere. One wag suggested the font, Verdana, might have been turned off on his computer. Helpful to that guy. Not me. I checked my font library and it, Verdana, was still alive. Another victim uninstalled/reinstalled the program. Didn’t work for him. Me either. Awhile back I was gifted with a brand spanking new fancy-smanshy bizillion bit Sony Vaio Windows 8 laptop but despite its Savant-like performance it is also accompanied with some maddening Tourettes-like tics . I suffered with this thing for a year with a Photoshop problem. Similar thing; a tool wouldn’t work. Sony and Adobe each pointed their fingers at one another. “It’s them”, they said. Then one day Photoshop began to play nice and it worked as it should. No clue as to what the fix was, only that the problem went away. Now I had this thing driving me nuts. While searching my machine for hours, and then days for a clue, I discovered an automatic update coincided with the same date that my measurement input problem started. Allowing a little time for consideration I finally decided to perform a system restore. I set the restart calendar to be the day before the update and wuddaya know? It’s working again! My Sketchup will again accept typed inputs in the measurement window. This is something that worked for me and is provided only as a suggestion. If you’re stuck this might work for you too.