I have notifications on the mail tile but when i clicked - "mail can't open" is on the screen

1. Have you connected Mail App to a exchange server?
2. Have you made any changes to the computer prior to this issue?

Follow the methods mentioned below and check if it helps.

Method 1: I would first suggest you to test the issue on a new user account. In the new Metro interface, you can find the Control panel App.

a) Click on the Control panel which brings main screen of control panel.
b) Find an option which is named as Users.
c) Click on the Users, you will be taken to a user screen, where you will find four options “change your password, create a picture password, create a pin and users".
d) Below the other users, you will find a button with + symbol. Click on it, you will be taken to the next screen.
e) In this screen, you can create a separate user account. If you have a Windows Live ID. You can use it to create an account.
f) If you don't have a Windows Live ID, you can click on the More login options. You can select a local account.
g) Fill the details in the local account, and click on Next.
h) A new user account will be created. Now, you can login with the new user account and check.

Method 2: If that does not help, uninstall and reinstall the Mail app.
Step 1: Follow the steps to uninstall the Mail app:
a. Right click the app that you want to uninstall.
b. Click on Uninstall in the task bar.
c. Then click on Uninstall button.

Step 2: Follow the steps to install the Mail app from the Store:
a. Click on Store.
b. Search for the app that you are looking for and click on the app and install it.