ease of access button not working at logon

Hi Anujsharma,

I understand how frustrating it could be when things do not work as expected. Please do not worry I will try my best to resolve it.

Method 1
Step 1: I would suggest you to boot the computer into safe mode and check if the issue persists.

Start your computer in safe mode
http://windows.microsoft.com/en-IN/windows7/Start-your-computer-in-safe-mode

Step 2: If the issue is fixed in safe mode, then I would suggest you to perform clean boot and remove the program that is causing the issue.

How to perform a clean boot to troubleshoot a problem in Windows Vista, Windows 7, or Windows 8
http://support.microsoft.com/kb/929135
Note: Follow step 3 from the clean boot article KB929135 to reset the computer to normal mode.

Method 2
I would suggest you to run SFC scan. SFC scan will scans all protected system files and replaces incorrect versions with correct Microsoft versions.

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

Method 3
Microsoft Safety Scanner
http://www.microsoft.com/security/scanner/en-us/default.aspx

Note: When you perform online virus scan you will lose some data that is affected by virus. Microsoft is not responsible for such data loss.

Hope this helps. Let us know the result.