Try killing all the related tasks and stopping the services first?

i cant find any services or tasks that would be related to it

In Services.msc have you got :

Symantec Endpoint Protection
Service Name: Symantec Antivirus
(net stop "symantec antivirus")

Symantec Management Client
Service Name: SmcService
(net stop SmcService / Start>Run: "smc -stop"

In Task Manager you will have rtvscan.exe and smc.exe ?

Perhaps you could also check your tamper protection settings incase you have a setting blocking you from stopping the services?

use cleanwipe to remove sep . and then scan with nss.exe before installing sep

 it is because of liveupdate.Restart the computer then try to un-install again.

Try deleting the following folders, if they exist and reboot the machine. Then try reinstalling SEP.

C:\Program Files\Symantec
C:\Program Files\Common Files\Symantec Shared
C:\Documents and settings\All Users\Application Data\Symantec

Let me know if this helps :-)

Try the manual removal

http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007073018014248

Hi I have uninstalled SEP Client 11 from my Windows XP using the ff guid:

http://service1.symantec.com/SUPPORT/ent-security....

Now I am having a problem installing SEP Client 10. The installation procedures goes fine until the end and prompts me for a scan schedule. But after everything finishes, the program does not appear in my installed programs.

Any help would be appreciated

Try scanning with nss.exe with latest signature. after this install sep.