hi there , yesterday i updated the avast free version like any day , but after i restart my system (Windows XP PRO )
i only could login and then it shows the desktop but wenn i klick anything then the system freez .
sry my english is not giid 
i got Windows XP Pro SP3
dell dimensions 5150
pentium 4 CPU
radeon graphics
and a dell keyboard
so i test the hardware of my pc to get sure it is ok , after the test it say anything is ok , so wenn i reeboot my system the screen shows me a warning the keybord get a error , so i changed it and try rebooting again but the same problem like say bevor
(i get to desktop but when klick anything it freeze the system)
so i use my backup software (acronis True Image )
and anything was working fine again , but whe i update the avast software the problem came back !!!
so i want tell you this so you can fix it.
if you need more information about my hardware like keyboard model .
then send me an mail i will edit this topic.
Greetz John