blank admin page

Could be anything, like white space, using the BOM, or ending php tags etc;

Without seeing the page it's hard to tell.

the page does not load any messages only a white space

it was working fine until the site went down because of a hosting problem on the server
when the hosting provider sorted that out and the website was live there was a message
which said php error in line 257 php cannot return a reference. i am paraphrasing because i cannot remember the exact words

i fixed that by going to the common php file and changed the code as recommended

with this next problem there are no messages so i do not know where to start.