Go to Solution.
Are you working in a single part file or an assembly?
If it is an assembly, is the selection scope set to "entire assembly"?
Try get Ctrl+L and than select your sheet body.
It could be Visible in View setting. Have you checked this?
Check that all the layers are set to "selectable" (i.e. the "visible only" option is turned off on each layer).
When I zoom in, one click can be selected.