COUNTERSTRIKE in game lockdown!! HELP THANK YOU SO MUCH!!!

to start with i have an asus p5p800 motherboard with a 3.2 processor. i also have an ati radeion 9800 pro 128 bit graphics card and a 450 watt power supply... now i have been playin counterstrike source on my computer and when i go online to play about every 1-5 minutes teh game locks up and it takes 20 seconds to start again.. i did a test on the main menu of counterstrike source and says im getting 96.8 fps.. and ive been using the lowest of all settings on a 17 inch flat screen lcd monitor.. my computer locking up should not be happening please anyone if u could help me i would greately appreciate it!