Hope this isn't stating the bleeding obvious, but you're not adjusting the levels on a new, blank layer by any chance?
(
drimble he'd been white, he'd been black,
Wed 30 May 2012, 22:37,
archived)
Ha, no.The levels weren't responding at all. The sliders wouldn't even move.
(
Fluffy elephants,
Wed 30 May 2012, 22:45,
archived)