Hey,
a. Was it working fine earlier?
b. Did you make any recent changes to your computer?
Having the Save As dialog appear on the Task Bar or having it make sure it is the top-most window would help.
Try performing System File Checker (SFC) scan on your computer. SFC tool scans system files and replaces incorrect versions of the system files by using the correct versions.
To run the System File Checker tool, follow these steps:
1. Click Start, and then type cmd in the Start Search box.
2. Right-click cmd in the Programs list, and then click Run as administrator. If you are prompted for an administrator password or confirmation, type your password or click Continue.
3. At the command prompt, the following line, and then press ENTER:
sfc /scannow
Check the below link for details:
How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7
**http://support.microsoft.com/kb/929833**
Also you may check if the issue persists in new user account.
Method 2: Create a New User Account
When troubleshooting a variety of issues, it can be useful to determine if the issue affects a specific Windows user account or all accounts. Follow the steps below to create a new user account in Windows Vista or Windows 7:
1. From the Start menu, choose **Control Panel.**2. Open Add or remove user accounts (If using the Classic View in Windows Vista, open User Accounts. Then open Manage another account).
3. Select Create a new account and follow the instructions to complete the account setup process.
4. Once the new account is created, choose Log Off from the Start menu.
5. Log into the newly created user account.
If the issue does not persist in the new user account then you may copy the files from the existing profile by following the steps mentioned in this link:
Fix a corrupted user profile**http://windows.microsoft.com/en-US/windows7/Fix-a-corrupted-user-profile**
Regards,
Divya R – Microsoft Support.