prob with the boot time scan

hello frds i am new user of avast

i am using avast 5.0.545 free version
in the avast anti virus boot time scan is not working

i am using hp dv6 with 64bit with windows7 home premium
can u plz help me in
working of the boot time scan in this avast

plz help me

Update your avast!
The latest version is 6.0.1203

avast 5 does not have boot time scan on 64bit systems…you need avast 6 for that