How to check a list column value is null in calculated column

=IF(NOT(ISBLANK([Column1])), IF(NOT(ISBLANK([Column2])),
IF([Column1]<=[Column2], "Success", "Failure"),""), "")

“Open with Explorer” tab showing as disabled in sharepoint 2010

Sometimes you might faced below errors when you try to open the documents from library by clicking 'Open with Explorer' tab.

Typical error messages:

• “Your client does not support opening this list with Windows Explorer.”
• This is control is currently disabled as shown in below image
• 

Resolution

Make sure that following service is started, by going: Click Start -> Control Panel -> Administrative Tools -> Services.  
Open the Properties of the WebClient Service. choose as start type: automatic . Restart the service . then check the site in IE

hope this helps...