Corrupt language file !
Use an old back up file.
Control panel, search for what you would expect to see on the white page. Difficult i know but its a clue to which file has gone corrupt on you.
Corrupt file
it could be as simple as a "," missing off the end of a line.
Quick fix.
Back up all your language files.
Restore with Ubb default files and see what happens.
Hope that helps.
