Did you modify it? You can go to your mw3 folder > players2 > plutonium.cfg, open it via npp preferably, search for r_aspectratio, change it to auto and search for r_mode, and set its value to your monitor's res, hit save and try launching the game again. You could also try setting r_displayMode to windowed (no border) and see if it launches the game now.
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