Can't login Admin

[jomagi]

Hi there!

 

I make a shop, customize it and allmost during one year don't do nothing, don't have ok to go full online!

Now I'm back to complete all and put full online.

 

The shop look ok at first glance but I can´t access admin page, I'm getting a

 

"Error 500: Internal Server Error

The server encountered an unexpected condition which prevented it from fulfilling the request.

The problem is on the server side, not with your browser or the address. Most probably, a certain service (e.g., Tomcat engine) is down. Please contact your webmaster."

 

What happen and how can I resolve that, It works fine at the time I leave it.

 

Thanks in advance.

 

osCommerce 2.2-rc2a / PHP 5.2.6