CCleaner and HiJackThis unusable !!

Hello to all,
someone can give some info or hint, on my notebook running Windows XP I cannot start neither ccleaner nor HiJackThis, if I open the directory explorer and stay with the mouse pointer on one of the mentioned files "something" kill the windows explorer so there is no way to start one of them.
I tried also to rename the file, ccleaner became xyz.exe and in this way I started the program but at the same time "something" kill it.
The antivirus doesn't find virus (I've McAfee, but I also tried with Norton from another notebook connected via LAN)

Any idea about that
Thanks in advance
Alessandro