If you are new to simulation, start with the latest ModelSim Intel FPGA Starter Edition (currently 2023.4). The interface has improved, and it's easier to find tutorials.
If you obtained ModelSim 10.5 from a friend or third-party (not recommended), here is how to check its integrity: modelsim 10.5 download
ModelSim*-Intel® FPGA Pro Edition 10.5c Release Notes File * ID 652698. * Date 2019-12-07. ModelSim*-Intel® FPGA Pro Edition 10.5b Release Notes File If you are new to simulation, start with