Program uninstalls at shutdown

I have tried three times to install a free version of CASecurity Suite and each time all the components install without a hitch except the antispyware which installs and then uninstalls when I shut down.
This computer is running xp media center version and has just been repaired after major virus and spyware infestation.
I have downloaded and run windows installer cleanup utility (msicuu2.exe) and that fixes things until I shutdown again.
Any suggestions would be greatly appreciated.
Thanks

 

Thanks so much for the prompt reply.
I might have to take your advice and install an alternate antispyware program but my concerns are:
1. the owner of this computer (my big sister) is tech challenged at best and the CA is provided free from her ISP as well as free support.
2. Posting a log seems to have a long backup time
3. I did the cleanup and used four of the suggested online scans as well as spybot and adaware and superantispyware and Ccleaner and trojan hunter. The other three components of the suite are installed and functioning.
4. I am wondering if the problem is a corrupt windows file that might mess up future installs