I just downloaded SolidWorks 2015 yesterday, I ran a Transient Thermal Simulation and I am getting a "HASTAR has stopped working" failure.

has the software ever worked before? if you're not sure, setup a really simple model of a block with convection and power, see if that help

if it does, the problem is setup or model specific, potentially software but not installation

once you narrow down the problem, simplify your analysis and see if that helps and build up from there