Computer Freezing Up

I had a cable modem installed, along with a network. My computer started to freeze at no speecif times, and during no specific tasks, just when it wanted to. It would freeze 4-5 times a day. (control,alt,delete does nothing) I figured I needed afirewall. It cut down on the freezing, but it is still happening.

My question: Do I need better firewall? Is the freezing due to my new set up and what is the best wy to stop the FREEZE!?