thanks for your input davey!
i think that the issue is not related to any startup 3rd party software.the fact is that,after runing defraggler on the system disk,vista does not automatically make any new restore point,the list is simply blank.
this issue do not happen with the vista's defrag utility. it deletes every restorepoint too,but after the defrag,vista automatically recreate one restore point.
this is quite odd,so at the moment i'm using defraggler on the other disks and vista's defrag utility only on the system disk.
hope someone @piriform can enlighten me on this. i'd like to use defraggler on the system disk too
thanks for your time davey!