Cannot acces to wp-admin/about.php

Hello there:

I have a problem accessing to the dashboard of my webpage,

Generally I access to my website with the following link

http://l4g.ch/wp-admin/about.php

But today I tried to do it and it does not work, instead it appears the following message

No input file specified.
I haven’t done any changes on the website on the last months, so I really cannot understand what happened.

I have read a few treats and tried to fix it, but haven’t got any positive result until now.

Any idea of how can I fix it , or in which direction to look?

Best Regards

Eloisa