Well you can use Task Manager to keep an eye on Memory usage and CPU usage, if either if these are bouncing up to 90%+ then its likely something that's running on the computer is causing it to freeze. If you view the processes tab you'll be able to see what's hogging up the systems resources - IF ANYTHING.
As for monitoring temperatures, I use HWMonitor myself. Great tool which will monitor your CPU, GPU and HDD temps. http://www.cpuid.com/softwares/hwmonitor.html