I was hoping you would say the mail screen takes up the whole page because then it would be an easy fix.
The only other thing I can suggest is uninstalling/reinstalling again, but instead of using the Windows uninstaller use Revo Uninstaller. This will allow you to also delete registry keys and folders, which sometimes get left behind when using Windows uninstaller.
If you have any mail you want to save, back it up first. Also back up your address book.
Here is how to use Revo Uninstaller:
1) First we download it from here:
Revo Uninstaller Free Version. You can skip this Step if you already have it installed. However, you may need to update it. If you have it installed already, and you need to update it, go ahead and open it up and click the AutoUpdate Icon next to Help. The use of this program makes registry changes based upon what you select for removal from the Registry. Before running Revo Uninstaller please run
ERUNT before proceeding to back up your registry in case you make a mistake.
2) Select the Program to remove from the list of programs and click the
Uninstall button:

3) After selecting the program you want to remove, and confirming you want to uninstall the program, then you will want to select the Advanced Option:

4) Click
Next. This will start the uninstaller for the application you picked. When the uninstaller is done, and it proves to be successful, and a reboot is required, then select
NO and continue the below steps.
5) Follow the prompts during the uninstallation of the application. Once it closes you will be at this window:

6) Click
Next again. Once the window is done scanning for files and other things that did not get removed, you will be presented with this window:

.
You will want to select only the bolded items, then click on
Delete. If any entries-usually the last thing listed and not in bold-have a + sign click on the + until you see more bolded items. Once done, click
Next.
If it asks you to delete other files, then do so,
but pay attention to the warnings.