Salam,
Sometimes, after patch or some miss configuration make our OWA down or something else. So, what we can do is to remove and recreate back virtual directory for OWA. Here is the step :
1) Identify all your virtual-directory using :
Get-owavirtualdirectory
2) Remove OWA virtual directory using :
get-owavirtualdirectory | ? {$_.OwaVersion -eq “Exchange2007”} | remove-owavirtualdirectory
3) Recreate back OWA virtual directory using :
new-owavirtualdirectory –owaversion “exchange2007” –name “owa(Default Web Site)”
Then test back your OWA. It will works fine.. 🙂