Can anyone tell me whats wrong with my mountain ash?

Some of its branches started dying

Here is a closer picture,I have another growing a few feet away will this one get the same thing?

Look for signs of ash borer.
http://www.aphis.usda.gov/publications/plant_health/content/printable_version/pub_pheab.pdf

All the ash trees have been cut down because of the bug around here. I hope it hasn't gotten that far east!

Check out some info on fire blight. Maybe that's what you have. It can be sprayed with copper sulphate. The branches with the dried up leaves should be trimmed off. I'm no expert, but we have had it here on Mountain Ash and crabapple trees.