Problems with second monitor

Hi all,

I have a MBP described bellow, and I have a problem, started after I changed the background image (I don't know if its had to do) to change each 15 minutes.

After this change, the second monitor started to be scratched, unreadable and freezing my MBP. Only solution was disconnect the mini port and force shutdown the machine. I tried this actions some times, but now, MBP doesn't recognize mini port any more. What might be happening?

OSX 10.9.5

2.5 GHz Intel Core i5

4 GB 1600 MHz DDR3

Intel HD Graphics 4000 1024 MB

Mini DisplayPort to DVI Adapter

Dell LCD monitor 22"

Thanks in advance.

Fabiano Oliveira