Why does my Bold 9900 have a black screen when it locks?

my phone recieved slight water damage so i left it for a couple of weeks, it now works fine until i lock it or it locks automatically, when i go to unlock the backscreen light comes on but screen stays black, ive tried updating software but still the same.
any help gratefully apreciated!!

If you had severe water damage, this sounds like an issue with the hardware and not necessarily the OS.

was thinkin that myself, i have a spare 9900 with a smashed front screen i could use for parts but im pretty clueless to be honest, maybes worth takin both for repairs!!