viruclean found at www.rizone3.com is better... catches more of viruses and malware than any I have found yet. It is free as well and there are many other nice programs there. It also might be a registry issue or a broken program.... Try ccleaner as well and do the registry repairs in it. It might do the trick. If that doesn't work, hit ctrl+alt+del when it locks up and check the task manager to see if there is a program that says not responding. If task manager does not function, my guess is windows boot file broke.... easiest fix is reinstall windows as a repair install (in anything but windows 7 that would mean reinstalling any installed software.... but windows 7 just repairs the broken bits).