Can't Reinstall Any Spybot S&D Version

[ralias]

I had Spybot S&D Vers 1.62. My Tea Timer corrupted, and would not show up at startup. I uninstalled Spybot S&D 1.62, and can not reinstall. I get an error indicating that I don't have administrative rights. A review of my administrative settings, in Windows XP 32-bit pro, suggest that I do have administrative rights.
How do I fix this problem?

The problem is not merely limited to Spybot S&D. I can not install other software, etc.

[tashi]

Hello ralias,

A review of my administrative settings, in Windows XP 32-bit pro, suggest that I do have administrative rights.
How do I fix this problem?

Did you elevate permissions on XP by right-clicking the Spybot S&D icon and then clicking on 'Run as Administrator'?

The problem is not merely limited to Spybot S&D. I can not install other software, etc.

You can't install software of any type? When did the problem start, do you recall a specific event.

How is the computer running in general, are there indications it might be infected?

Please list any security software already installed and which Service Pack is on XP Pro.

Best regards.