Solved! Latitude D630 key not working

Try taking off the key and see if there is anything below it, i.e. dirt, etc.. that could be impeding it.
 
Solution
thats an old laptop - more than likely the keyboard needs to be replaced. They are not the most reliable after 2-4 years. You might get it to work by carefully placing some lubricant in the key, but it wont last long...