macbook air lion 10.7.5

Dear friends,

I have lost the ability to do a double click to open a file or folder, a single click will highlight but then i have to use command 'o' - i never used to have this problem and have played about a bit on track pad - system preferences - can anyone hlelp?

Are you having a drag-stuck/lock issue? Meaning can you drag and drop? When I was having trouble with stuff like this - it was because the mouse wasn't letting go of selected data.
https://discussions.apple.com/thread/2539560?start=0&tstart=0