Hmm, seems like it can be done without installing mcetools.
GConf has /system/osso/dsm/display/inhibit_blank_mode key.
Something about this key:
Command to set needed value:

such friends, I have the same problem and I have done everything here ah said but no solution about it ... I do not like to restore the factory settings because they would lose a lot of information but unfortunately I'll have to do to see if that solves my problem because with the commands mentioned in the forum have not worked for me ... what can I do besides that friends and not restore the factory settings?:confuso:

Anything is possible, but if the above didn't work, I would be more inclined to think you have a hardware problem.

Gabriel85, did to you try both methods?
What does 'mcetool --status' prints? (at this moment my mcetool prints 'disabled' for blank inhibit and all works fine).
What 'gconftool --get /system/osso/dsm/display/inhibit_blank_mode' prints? (my current value is 0 and all works fine).

the friend really do not understand any of it, not how to get or do what you say you me about those command ... tell me how could perform these commands? Thanks for the reply in advance ...

My gconftool --get /system/osso/dsm/display/inhibit_blank_mode' prints... is "0".... and even still you giving me this problem the screen turns black when I answer a call or perform ... what could I do?

Same as RANBAXY for me: just Restore the settings !
I got the issue after tuning status bar through n9 qtweak. I ran Restore the Settings (in Reinit section of System setting) and solved it. Not painful. I just lost the folders in homescreen.