If your computer has not enough memory and you are using Windows Vista, join the club. VISTA is crap and hangs most computers. It needs a lot of Virtual Memory to swap data from RAM to the HDD. Its possible that the Virtual memory allocated to your new HDD is insufficient for your software requirements. Try increasing the Virtual memory allocation. Also examine your list of startup programs and disable any you do not really need at startup
I cant' really say more without knowing your computer.
The OS is Windows 7 w/4 gigs of RAM. I've already tried the disabling of processes that aren't necessary ( Itunes, Steam, Games etc...) and that doesn't seem to help. The computer usage is down to about 24% and it still freezes.