Make sure , no Java updates were applied to the machine that you are 
having the issue on, try accessing the NMC from different machine, NMC has 
specific requirements for Java ( 1.4.2-for 7.3.3).
I see the problem on workstations often where java update 5 or 6 are 
applied, uninstalling them will work where NMC window is not behaving 
properly in certain environment.
Lastly, double check if its not any IE settings that could affect it.
HTH

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