Internal Server Error

I hadn’t really paid much attention, but now that I think about it, as I have upgraded WordPress versions, I have been losing more and more Admin pages to Error 500: Internal Server Error (using 1and1). Now that I have version 3.0, I cannot get into ANY of my admin pages. Help! I don’t know how to fix this, but (obviously) need to have access to my Admin area.

Thanks so much for your help.