check your task manager performance
monitor the chart and see what is spiking when it freezes (or whether the memory is always almost full)
When the memory is always full it will do a lot of swapping which slows the system a lot.
Run the resource monitor and look through everything to see if there's anything unusual.
Also check your disk with HDTune look at the SMART and see if there failures or high warnings.
(Hope you are running Windows 7)