Hello there,
I hope while u created ur project, u did specify the simulator as Modelsim, SE XE or whatever version u have, And i hope u have proper licence from modelsim as well, ie the starter edition licence or the hardware lock drivers properly intalled and so on...
Then i again hope that u have included the testbench as "for simluation"
Then i hope from the action menu , u have selected behavioural simulation,
Then u will be able to see the test ebnch in the sources list in the project explorer, and in the process explorer, u wil see the simulation options..and there if u have selected modelsim simulator, u will see the "Modelsim" or Xilinx ISE as the option
Please dont feel offended if u r expert level is above all these and u have followed all the above steps.. Its just that i cant judge or try to judge u r expertise level from this distance , and can only follow the basic step by step confirmation...
If all these things are done and u r absolutely sure that there is no probs with ur source testbench and the other source files, we can suspect ur installation.